UX Guide: add comment and discussion to copy
Based on conversation here: https://gitlab.com/gitlab-org/gitlab-ce/issues/24378#note_18813332
Adding documentation to the UX Guide around comment and discussion terminology
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Based on conversation here: https://gitlab.com/gitlab-org/gitlab-ce/issues/24378#note_18813332
Adding documentation to the UX Guide around comment and discussion terminology