Update docs to match new markdown style guide 2
Created by: cirosantilli
Same as https://github.com/gitlabhq/gitlabhq/pull/6863 but I deleted my fork before merge.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Created by: cirosantilli
Same as https://github.com/gitlabhq/gitlabhq/pull/6863 but I deleted my fork before merge.