Update permissions docs (!19858) · Merge requests · GitLab.org / GitLab FOSS · GitLab

Achilleas Pipinellis - OOO until November 25th (parental leave) requested to merge docs/permissions into master Jun 14, 2018

What does this MR do?

Update permissions docs and port sections from EE.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/45222