Adds "comments on snippets" to doc
What does this MR do?
From CE https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11563
Edited by Achilleas Pipinellis
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
From CE https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11563