Update issue-related docs
See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html
What does this MR do?
Port changes introduced by https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2330
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
See the general Documentation guidelines http://docs.gitlab.com/ce/development/doc_styleguide.html
Port changes introduced by https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2330