Update this project labels descriptions for issues and MR's
Since labels are applicable to both issues and MR's, their description should be adapted to be applicable to both cases. Currently, on GitLab CE, most labels description refers solely to issues.
Example: gitlab-ce~3630472 — “Issues with this label are regressions…”
Related
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5371
/cc @rymai