A SUPPORT STRUCTURE FOR AN O-LOCK Field The present disclosure relates to a support structure for insertion into an O-lock, an O-lock that comprises the support structure and a sheath and a method of assembling an O-lock. Background Various designs of stand-alone locks, such as O-locks and D-locks, exist for securing articles to other articles. Stand-alone locks are regularly used, for example, for securing bicycles, scooters, pushchairs and other outdoors equipment to permanent structures such as bicycle parking racks, fences or lamp posts in order to reduce the likelihood of such equipment being stolen. Some O-locks are used on the back of wheeled articles, such as bicycles, in order to secure the wheel to the article when locked. This can prevent thieves from wheeling away a stolen articles. Such stand-alone locks generally make use of physically actuated key locks. Assembly of stand-alone locks makes use of screwing, welding or riveting two halves of a sheath (casing) together after the insertion of any components that are needed to be contained within the casing. A shackle is then able to move between a locked position and an unlocked position. Summary According to a first aspect of the present disclosure, there is provide a support member for insertion into a sheath of an O-lock, the sheath comprising an open ring-shaped casing having a gap between a first end and a second end for bridging by a shackle, wherein the support member comprises at least a first arcuate segment and a second arcuate segment, wherein at least the first arcuate segment is sized to fit between the first and the second end of the sheath in an orientation for sliding into the sheath. In one or more embodiments, the support structure may further comprise a connection portion between each pair of arcuate segments wherein the connection portion is configured to connect the arcuate segments together and wherein each connection portion is configured to provide for sequential insertion of the arcuate segments into the sheath such that each of the arcuate segments are connected together when fully inserted into the sheath. In one or more embodiments, each connection portion may be configured to provide for deflection of the second arcuate segment relative to the first arcuate segment such that, during insertion of the first arcuate segment into the sheath via the opening, the second arcuate segment can be deflected away from the first arcuate segment. In one or more embodiments, the connection portion between the first arcuate segment and the second arcuate segment may be a hinged coupling. In one or more embodiments, the connection portion that connects the first arcuate segment to the second arcuate segment may be a resiliently deformable connection portion that provides for the deflection of the second arcuate segment relative to the first arcuate segment. In one or more embodiments, the first arcuate segment may be releasably connectable to the second arcuate segment and wherein the connection portion provides for the releasable connection of the first arcuate segment to the second arcuate segment. In one or more embodiments, at least one of the first arcuate segment and the second arcuate segment may comprise one or more of: a power source chamber shaped to receive a power source therein; a motor chamber shaped to receive a motor therein; a printed circuit board chamber shaped to receive a printed circuit board therein; and a shackle chamber sized to receive a shackle therein. According to a second aspect of the present disclosure, there is provided an O-lock comprising: a sheath comprising an open ring-shaped casing having a gap between a first end and a second end for bridging by a shackle; and a support structure of any preceding claim. In one or more embodiments, the O-lock may further comprise: a power source; a printed circuit board that comprises a controller; and a motor, a shackle configured to be movable between a locked position and an unlocked position. wherein the power source is configured to provide power to the controller on the printed circuit board, wherein the controller is configured to drive the motor and wherein the motor is configured to drive the shackle between the locked position and the unlocked position. According to a third aspect of the present disclosure, there is provided a method of assembling an O-lock comprising receiving a sheath comprising an open ring-shaped casing having a gap between a first end and a second end for bridging by a shackle; receiving a support structure comprising at least a first arcuate segment and a second arcuate segment, wherein at least the first arcuate segment is sized to fit between the first and the second end of the sheath in an orientation for sliding into the sheath; locating the first arcuate segment substantially in the gap between the first end and the second end of the sheath; inserting the first arcuate segment into the first end of the sheath; subsequently inserting the second arcuate segment into the first end of the sheath. Brief Description of the Drawings One or more now be described by way of example only with reference to the accompanying drawings in which: Figure 1 shows an example embodiment of an O-lock having a shackle in a locked position; Figure 2 shows another example embodiment of an O-lock having a shackle in an unlocked position; Figure 3 shows an example embodiment of a support structure; Figure 4 shows an example embodiment of a support structure being inserted into a sheath of an O-lock; and Figure 5 shows an example method according to the present disclosure. Detailed Description The present disclosure relates to a support member for insertion into an O-lock wherein the support structure comprises a structure such that it can be inserted into a sheath of the O-lock via a first end of the O-lock. An advantage of this is that, by inserting the support structure via the first end of the sheath, there is no need to initially form the sheath in two parts that are later welded together to form the final sheath. Instead, the sheath can be formed of a single, monolithic, piece of material. This may reduce physical vulnerabilities in the sheath which could be exploited by thieves to break the O-lock. Further, by removing the need for a welding step, the associated energy and materials required to perform that step are not necessary and, as such, the final product can be produced more energy and resource-efficiently. In one or more embodiments, the O-lock may be a remotely operated O-lock that does not require a physical key to actuate movement of the shackle from the unlocked position to the locked position. For example, the O-lock may be a Bluetooth-operated O-lock, however, any other suitable remote signal activation method may be used. The absence of a physical lock configured to receive a physical key may remove another component which would otherwise require the sheath to be formed in two parts prior to insertion of various components into the sheath and subsequent welding of the sheath together. In some embodiments, the sheath of the O-lock may comprise a keyhole. The design of the product without the need to use welding, riveting or screwing of two halves of the sheath together may also be particularly aesthetically pleasing. Figures 1 and 2 show an example O-lock 100 according to the present disclosure in an unlocked configuration and a locked configuration, respectively. The O-lock 100 comprises a sheath 101 which is an open ring-shaped casing extending between a first end 102 of the sheath and a second end 103 of the sheath. That is, the sheath 101 has a substantially C- shaped tubular structure which may be described as an open toroid. The arcuate shape of the sheath 101 defines a gap 105 between first end 102 and the second end 103 of the sheath for bridging by a shackle 104. The sheath 101 and the gap 105 for bridging by the shackle 104 together define a closed ring. Thus, when a shackle 104 of the O-ring 100 is in a locked position, as shown in figure 2, the sheath 101 and the shackle 104 together define a closed ring. Where the closed ring defines a circle of 360 degrees, the angle defined by the gap 105 between the first end 102 of the sheath and the second end 103 of the sheath may be from 60 – 100 degrees. In other examples, the angle of the gap 105 may be between 70 and 90 degrees. In yet other examples, the angle 105 may be substantially 80 degrees. The sheath 101 comprises a hollow interior into which the support structure can be inserted. The O-ring 100 may further comprise a shackle receiving end cap 106 which extends partially into the sheath 101 in order to close the first end 102 of the sheath. The shackle receiving end cap 106 comprises a well into which the shackle 104 can extend when the shackle 104 is in the locked position. By providing the well of the shackle receiving end cap 106 for the shackle to extend into, the shackle 104 and sheath 101 can define a closed loop when the shackle 104 is in the closed position. In this way, there is no risk of there being a gap between the end of the shackle 104 and the first end 102 of the sheath that a potential thief could exploit to force the O-lock 100 open. The O-lock 100 may further comprise a shackle providing end cap 107 which is configured to close the second end 103 of the sheath 101. The shackle providing end cap 107 comprises a shackle aperture through which the shackle 104 extends when moving from the unlocked position to the locked position. In some examples, the shackle 104 may be housed entirely within the sheath 101 when in the unlocked position and in other examples, the shackle 104 may protrude slightly from the shackle aperture when the shackle 104 is in the unlocked position, as in the embodiment showed in figure 1. The shackle receiving end cap 106 and the shackle providing end cap 107 may each be configured to have space for an O-ring to be located on their inner edges such that they provide for a hermetic seal, or near-hermetic seal, to the sheath 101 when they are closed in place over the first end 102 and second end 103 of the sheath respectively. The sheath 101 may further comprise one or more brackets 108 which are configured to provide for affixing the O-lock 100 to an object to be locked. For example, the brackets 108 may allow the O-lock 100 to be permanently affixed to a bike so that a bike wheel can be selectively locked or unlocked. The brackets 108 may comprise apertures through which affixment means, such as screws can be placed. The O-lock 100 does not necessarily require the brackets 108 in order to provide for functional locking of one object to another. The sheath 101 may further comprise an affixment aperture 110 through which affixment means, such as a screw, can be inserted. The provision of the affixment means through the affixment aperture 110 may allow for the affixment of the support structure within the sheath 101 once the support structure is fully inserted into the sheath 101. By providing only a single affixment aperture 110, the ease of assembly and disassembly is improved. Further, the provision of a single affixment aperture 110 also limits the possible apertures for the ingress of dust or water into the sheath 101. The sheath 101 may further comprise a tab slot 111 which extends along an arcuate longitudinal length of the sheath 101. The tab slot 111 provides space for a tab 112 which forms part of the shackle to slide from a first position to a second position. The tab 112 is in the first position when the shackle 104 is in the unlocked position and the tab 112 is in the second position when the shackle 104 is in the locked position. The tab 112 may provide manual manipulation and actuation of the shackle 104 when it is not locked in place by other means. For example, the tab 112 may be useful for helping to insert or remove the shackle 104 when assembling or disassembling the O-lock 100. Figure 3 shows an example support structure 300 for insertion into the sheath 101 of the O- lock 100. The support member 300 comprises at least a first arcuate segment 301 and a second arcuate segment 302, wherein at least the first arcuate segment 301 is sized to fit between the first end 102 and the second end 103 of the sheath in an orientation for sliding into the sheath 101. That is, at least the first arcuate segment 301 may have an arcuate length that is shorter than arcuate gap 105 between the first end 102 of the sheath and the second end 103 of the sheath such that at least the first arcuate segment 301 can be located in the gap 105 and then slid into the first end of the sheath 101. In some embodiments, each of the arcuate segments 301, 302 may have arcuate lengths that are shorter than the arcuate gap 105 between the ends of the sheath 101 for bridging by a shackle 104. In some embodiments, such as the one shown in figure 3, the support structure 300 may comprise more than two arcuate segments such as three, four or five arcuate segments. The arcuate segments 301, 302 are configured to be sequentially inserted into the sheath 101. One or more of the arcuate segments 301, 302 may be rigid arcuate segments that are substantially inflexible under normal use conditions. The rigid arcuate segments may provide for the necessary support for components which are housed in chambers in the arcuate segments 301, 302. In some embodiments, one or more arcuate segments may be flexible arcuate segments that can, themselves, be deformed or deflected during insertion into the sheath 101. Such flexible arcuate segments may have an arcuate length that is greater than the gap 105 between the first and second ends of the sheath 101, as they may be sufficiently deformable to allow for insertion into the first end 102 of the sheath 101 during assembly. Such flexible arcuate segments may not be suitable for housing components such as a power source, a PCB or a motor, as the segments may not provide for the required support for these components during insertion into the sheath 101. Such flexible arcuate segments may be suitable for comprising a shackle chamber 303, however, as the shackle 104 may be inserted into the sheath 101 prior to insertion of the support structure 300 and the support structure 300 may progressively cradle the shackle 104 in the shackle chamber 303 as the support structure 300 is inserted in to the sheath 101. In other embodiments, all of the arcuate segments 301, 302 may be rigid arcuate segments. An arcuate longitudinal length of the support structure 300 may be defined as the length of the partial loop defined by the support structure 300 through the cross-sectional centre of the support structure 300. That is, the arcuate longitudinal length may be defined as π (pi) multiplied by the diameter (d) of the circle defined by the arc of the centre of the cross-section of the support structure 300 multiplied by the circular angle (α) through which the support structure 300 extends in degrees divided by 360 degrees: ^{^ ^^^^^^^^^^ ൌ ^^^ ൈ} ͵ _^^ The arcuate longitudinal length is defined here in terms of the circle defined by the centre of the cross section of the support structure 300. It will be appreciated, therefore, that the maximum length of the outer edge of the support structure 300 can be calculated using the same equation but by replacing “d” with “d + r” where “r” is the radius of the cross-section of the support structure 300. In the case where the cross-section of the support structure 300 is not circular, “r” may be the greatest distance from the centre of the cross-section of an edge of the cross-section. The cross-sectional dimensions of the support structure 300 may be substantially the same as, or only slightly less than, the dimensions of the internal cross-sectional dimensions of the hollow portion of the sheath 101 such that the support structure fits tightly within the sheath 101. In this way, the support structure 300 will not have space, or not have much space, to rattle around within the sheath 101. For example, the cross-sectional dimensions of the support structure 300 may be 99%, 97% or 95% of the dimensions of the internal cross- sectional dimensions of the hollow interior of the sheath 101. Any other suitable dimensions may be used that are suitable to provide a support structure 300 that is held snuggly within the sheath 101. The total arcuate length of the support structure 300 is greater than the gap 105 between the first end 102 and the second end 103 of the sheath 101. By way of example only, the arcuate length of the support structure 300 may be from 70% to 95% of the length of the sheath 101. The support structure 300 may comprise one or more chambers shaped and sized to receive a plurality of different components. In some examples, a subset of the arcuate segments may comprise such chambers while in other amendments, each segment 301, 302 may comprise at least one chamber. For example, the support structure 300 may comprise one or more of: - A power source chamber 308 shaped to receive a power source therein; - A motor chamber (not shown) shaped to receive a motor therein; - A printed circuit board (PCB) chamber (not shown) shaped to receive a printed circuit board therein; and - A shackle chamber 303 sized to receive a shackle therein. In some examples, each of the above-listed chambers 303 may be present within the support structure 300. Each chamber 303 may be formed at least partially within one of the arcuate segments 301, 302. In other examples, some of the components may be sized such that the corresponding chamber 303 extends through several of the arcuate segments 301, 302. For example, the shackle chamber 303 may extend through a subset of the arcuate segments 301, 302 or all of the arcuate segments 301, 302 in order to provide sufficient space for the shackle 104 when in the unlocked position. The motor chamber and PCB chamber may be located on an opposing side of the support structure 300 to the shackle chamber 303. The power source chamber 308 may be formed in the final arcuate segment of the support structure 300 and may be configured such that the power source stored within the chamber abuts the well of the shackle receiving end cap 106. In some examples, chambers may not be required for each of these components and, in some instances, a power source, a motor or a circuit board may not be located within he support structure 300 but, instead, may be integral with the sheath 101 of the corresponding O-lock 100 or may be provided externally. In this disclosure, chambers 303 are gaps, cut-outs or hollows which provide space for the variously listed components. The chambers 303 may be configured to receive particular components by being sized such that the components are housed and retained within the chamber. The components may be retained within the chamber, for example, by way of a friction or push-fit and, in order to achieve this, the chambers may be sized to receive the corresponding components tightly or snuggly therein. The shackle chamber 303 may not be configured to tightly or snuggly contain the shackle 104 and, instead, may be sized to cradle and guide the shackle 104. One or more of the arcuate segments 301, 302 may further comprise one or more channels (not shown) that are configured to provide for electrical connection between a plurality of the components housed in chambers of the support structure. For example, the channels may provide for electrical connection between the power source chamber 308, the motor chamber and the printed circuit board chamber. The channels may provide for electrical connection by providing space for wires to extend therethrough to connect the various components. In other examples, the channels may comprise electrically conductive tracks that can provide for the electrical connection between components. The shackle receiving end cap 106 may be configured to fit over a first end 304 of the support structure 300 when the shackle receiving end cap 106 is inserted into the first end 102 of the sheath 101. This may provide for sealing of the first end 102 of the sheath 101 and assist in ensuring that the interior portion of the sheath 101 is resistant to the ingress of water or dust. Similarly, the shackle providing end cap 107 may be configured to fit over a second end 305 of the support structure 300 when the shackle providing end cap 107 is inserted into the second end 103 of the sheath 101. This may provide for sealing of the second end 103 of the sheath and assist in ensuring that the interior portion of the sheath 101 is also resistant to the ingress of water and dust. The shackle providing end cap 107 may be sized and shaped in a complementary manner to the second end of the sheath wherein the complementary size and shape of the shackle providing end cap and the sheath interoperate to prevent the shackle providing end cap from being rotated relative to the sheath. The support structure 300 may comprise a connection portion 306 between each pair of arcuate segments 301, 302. The connection portion 306 may be configured to connect the arcuate segments 301, 302 together such that each of the arcuate segments 301, 302 are connected together when fully inserted into the sheath 101. The connection portions 306 are further configured to provide for the sequential insertion of the arcuate segments 301, 302 into the sheath 101. It is important that the arcuate segments 301, 302 are connected together when fully inserted into the sheath 101 and particularly so in examples where the arcuate segments 301, 302 fit snuggly within the sheath 101. In examples where the arcuate segments 301, 302 fit snuggly within the sheath 101, it may be difficult or impossible to remove the arcuate segments 301, 302 from the sheath via one of the first end 102 or the second end 103 of the sheath if the segments 301, 302 are not connected together. By connecting the segments 301, 302 together, one can pull at one end of the support structure 300 in order to remove the entire support structure 300. The connection portions 301, 302 may be configured to provide for sequential insertion of the arcuate segments 301, 302 into the sheath 101 in a plurality of different ways while still providing for connection of the arcuate segments 301, 302 while inserted in the sheath 101. The example of figure 3 and figure 4 provide an example wherein the connection portions 306 are portions of narrow material that allow for the relative deflection of the adjoining arcuate segments 301, 302. The narrow portions of material may be sufficiently resiliently deformable that they can be articulated in order to provide a necessary deflection of the arcuate segments 301, 302 relative to each other. That is, the connection portions 306 are resiliently deformable connection portions 306 that provide for the deflection of the second arcuate segment 302 relative to the first arcuate segment 301. Figure 4 shows an example of a first arcuate segment 301 that is partially inserted into the sheath 101 while a second segment 302 is deflected away from the plane of the sheath so that the support structure 300 as a whole is not blocked from being inserted by the second end 103 of the sheath 101. The plane of the sheath may be defined as the plane through which the centre of the cross-section of the sheath 101 extends through the whole sheath 101. By way of this embodiment, the first arcuate segment 301 can be placed between the first and second ends 102, 103 of the sheath 101 prior to insertion and the second arcuate segment 302 can be deflected (bent) away from the first arcuate segment 301 in order to avoid abutting the second end 103 of the sheath 101. Once the first segment 301 is inserted into the first end 102 of the sheath 101, the second arcuate segment 302 will have space between the first and second ends 102, 103 of the sheath 101 to align itself in the plane of the sheath 101. This allows the second arcuate segment 302 to be inserted into the sheath 101 while the third arcuate segment 307 is deflected away from the second arcuate segment 302. This process can be repeated sequentially with each arcuate segment 301, 302, 307 until the entire support structure 300 has been inserted into the sheath 101. In this embodiment, the support structure 300 may be a single monolithic (unitary) structure. This may provide for ease of manufacture in a single point and provide for a reduced complexity in the manufacture compared to support structures 300 comprised of a plurality of parts. In an alternative embodiment, each connection portion 306 may be a hinged coupling which is configured to allow for the deflection of subsequent segments from preceding segments out of the plane of the sheath 101. A hinged coupling may be more complex and expensive to manufacture than a narrow and deformable material connection, but it may make it easier to deflect the arcuate segments 301, 302, 307away from each other. In yet another example embodiment, at least the first arcuate segment 301 may be releasably connectable to the second arcuate segment 302 and the connection portion 306 may provide for the releasable connection of the first arcuate segment 301 to the second arcuate segment 302. The first arcuate segment 301 may be releasably connectable to the second segment 302 by a connection portion such that, during insertion of the support structure 300 into the sheath 101 via the opening, the second segment 302 can be detached from the first segment 301 until the first arcuate segment 301 is sufficiently inserted into the sheath 101 to provide space for the second arcuate segment 302 between the first and second ends 102, 103 of the sheath 101. In particular, the connection portion 306 between the first arcuate segment 301 and the second arcuate segment 302 may comprise a first segment connection portion and a second segment connection portion wherein these two portions are configured to be releasably coupled together to provide the connection portion in full. The first segment connection portion and second segment connection portion may comprise co-operative connection means such as: co-operative snap-fit connections; corresponding fixing holes for receiving screws, pins or other fixing articles; or another type of releasable connection portion. In other embodiments, each of the arcuate segments may be releasably connectable to neighbouring arcuate segments by any of these methods. When the O-lock 100 is assembled, the shackle 104 may be configured to be movable between a locked position and an unlocked position. The shackle may be manually moved from the locked position to the unlocked position. Once the shackle reaches the locked position, it may latch in place. The motor may be provided to release the shackle from the locked position upon actuation of the motor. Actuation of the motor may occur in response to the receipt by a controller on the PCB of a release signal. The power source housed in the power source chamber 308 may provide power to a controller on the printed circuit board, housed in the PCB chamber, wherein the controller is configured to control the motor. The provision of a support structure 300 according to the present disclosure may facilitate the recyclability of the O-lock 100 as a whole. By providing the support structure 300 that can be inserted as described, the support structure 300 can also be removed in a corresponding manner. This means that the support structure 300 and all of the components that it supports can be easily removed from the sheath 101, thereby separating out parts of the O-lock 100 that are formed from different materials. Thus, not only does the support structure 300 of the present disclosure provide for easier assembly of an O-lock 100 and increased security against tampering, it also provides a more sustainable product. This ease of removal of the sheathed parts may also result in an O-lock that is easier to repair, and thereby reuse, compared to other examples. Figure 5 shows an example method 500 of assembling an O-lock. The method comprises receiving 501 a sheath comprising an open ring-shaped casing having a gap between a first end and a second end for bridging by a shackle; receiving 502 a support structure comprising at least a first arcuate segment and a second arcuate segment, wherein at least the first arcuate segment is sized to fit between the first and the second end of the sheath in an orientation for sliding into the sheath; locating 503 the first arcuate segment substantially in the gap between the first end and the second end of the sheath; inserting 504 the first arcuate segment into the first end of the sheath; and subsequently inserting 505 the second arcuate segment into the first end of the sheath. In order to locate the first arcuate segment in the gap between the first end and the second end of the sheath, the second arcuate segment may be deflected away from the first arcuate segment about a connection portion arranged between the first arcuate segment and the second arcuate segment. In other embodiments, in order to locate the first arcuate segment in the gap between the first end and the second end of the sheath, the second arcuate segment may be disconnected from the first arcuate segment prior to location of the first arcuate segment in the gap and subsequently reconnected to the first arcuate segment once the first arcuate segment is either entirely or mostly inserted into the sheath.