Add note on editing comments for mentions

doc/user/discussions/index.md

@@ -112,12 +112,27 @@ you can reply to comments by sending an email.
 
 You can use [Markdown](../markdown.md) and [quick actions](../project/quick_actions.md) in your email replies.
 
-## Who can edit comments
+## Edit a comment
 
 You can edit your own comment at any time.
-
 Anyone with at least the Maintainer role can also edit a comment made by someone else.
 
+To edit a comment:
+
+1. On the comment, select **Edit comment** (**{pencil}**).
+1. Make your edits.
+1. Select **Save changes**.
+
+### Editing a comment to add a mention
+
+By default, when you mention a user, GitLab [creates a to-do item](../todos.md#actions-that-create-to-do-items)
+for them, and sends them a [notification email](../profile/notifications.md).
+
+If you edit an existing comment to add a user mention that wasn't there before, GitLab:
+
+- Creates a to-do item for the mentioned user.
+- Does not send a notification email.
+
 ## Prevent comments by locking an issue
 
 You can prevent public comments in an issue or merge request.

doc/user/profile/notifications.md

@@ -21,11 +21,14 @@ that happen there.
 You might receive notifications for one of the following reasons:
 
 - You participate in an issue, merge request, epic, or design. You become a participant when you comment
-  or edit, or someone mentions you.
+  or edit, or someone mentions <sup>1</sup> you.
 - You've [enabled notifications in an issue, merge request, or epic](#notifications-on-issues-merge-requests-and-epics).
 - You've configured notifications for the [project](#change-level-of-project-notifications) or [group](#group-notifications).
 - You're subscribed to group or project pipeline notifications via the pipeline emails [integration](../project/integrations/overview.md).
 
+1. GitLab doesn't send a notification when
+   [a comment is edited to include a user mention](../discussions/index.md#editing-a-comment-to-add-a-mention).
+
 NOTE:
 Administrators can block notifications, preventing them from being sent.