Mention the privacy issue fixed by GitLab 8.6.2
Addresses the following concern: https://gitlab.com/gitlab-org/gitlab-ce/issues/14607#note_4520389
/cc @rabbitfang
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Addresses the following concern: https://gitlab.com/gitlab-org/gitlab-ce/issues/14607#note_4520389
/cc @rabbitfang