Improve markdown
Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4975 (thanks @sheerun) with small changes on top
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4975 (thanks @sheerun) with small changes on top