Update doc for write-access deploy keys
This was pointed out by @bbodenmiller at https://gitlab.com/gitlab-org/gitlab-ce/issues/1376#note_24150056
Current doc does not mention any write access.
This was pointed out by @bbodenmiller at https://gitlab.com/gitlab-org/gitlab-ce/issues/1376#note_24150056
Current doc does not mention any write access.