Docs: notify users when MR is marked ready

Adds basic cross-linking and information to the table that explains
what notifications are sent and when.

doc/user/profile/notifications.md

@@ -207,6 +207,7 @@ epics:
 | Fixed pipeline ([introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/24309) in GitLab 13.1.)    | The author of the pipeline. Enabled by default. |
 | Merge merge request    |         |
 | Merge when pipeline succeeds ([introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/211961) in GitLab 13.4) | Author, Participants, Watchers, Subscribers, and Custom notification level with this event selected. `Note:` Custom notification level is ignored for Author, Watchers and Subscribers   |
+| Merge request [marked as ready](../project/merge_requests/drafts.md) (introduced in [GitLab 13.10](https://gitlab.com/gitlab-org/gitlab/-/issues/15332)) | Watchers and participants |
 | New comment            | Participants, Watchers, Subscribers, and Custom notification level with this event selected, plus anyone mentioned by `@username` in the comment, with notification level "Mention" or higher |
 | New epic               |         |
 | New issue              |         |

doc/user/project/merge_requests/drafts.md

@@ -57,6 +57,10 @@ When a merge request is ready to be merged, you can remove the `Draft` flag in s
   in a comment in the merge request. This quick action is a toggle, and can be repeated
   to change the status back. This quick action discards any other text in the comment.
 
+In [GitLab 13.10 and later](https://gitlab.com/gitlab-org/gitlab/-/issues/15332),
+when you mark a merge request as ready, notifications are triggered to
+[merge request participants and watchers](../../profile/notifications.md#notifications-on-issues-merge-requests-and-epics).
+
 ## Include or exclude drafts when searching
 
 When viewing or searching in your project's merge requests list, you can include or exclude