Revert "Removed github descriptor. This was noted as deprecated and removed from the documentation on 28 Feb 2013 and is unlikely to be in use anywhere. For users who are still utilizing this descriptor, they can switch to a git descriptor."

This reverts commit 3249820eb8641082c38cdadd861bf31b2b8f5b36.
#25437 Removed github descriptor. 
This was noted as deprecated and removed from
the documentation on 28 Feb 2013 and is unlikely to be in use anywhere.
For users who are still utilizing this descriptor, they can switch to a
git descriptor."