added section for versioning to mrtk dev doc guide
added section for versioning to mrtk dev doc guide

killerantz/HoloToolkit-Unity,vladkol/MixedRealityToolkit-Unity,DDReaper/MixedRealityToolkit-Unity,vladkol/MixedRealityToolkit-Unity,killerantz/HoloToolkit-Unity,vladkol/MixedRealityToolkit-Unity,killerantz/HoloToolkit-Unity,killerantz/HoloToolkit-Unity