What does this MR do?
Updates documentation to note that GitLab only includes Fog libraries for a subset of available storage drivers.
Are there points in the code the reviewer needs to double check?
Documentation only; please check to make sure the libraries I've listed are correct. The applicable line in the Gemfile is linked.
Why was this MR needed?
The documentation is ambiguous as to whether all the Fog storage drivers are available; they aren't.