added common errors section to dev docs
added common errors section to dev docs

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