Add info about closing / deleting merge requests

doc/user/project/merge_requests/index.md

@@ -76,6 +76,35 @@ can assign, categorize, and track progress on a merge request:
 - [**Notifications**](../../profile/notifications.md): A toggle to select whether
   or not to receive notifications for updates to a merge request.
 
+## Close a merge request
+
+If you decide to permanently stop work on a merge request,
+GitLab recommends you close the merge request rather than
+[delete it](#delete-a-merge-request). Users with
+Developer, Maintainer, or Owner [roles](../../permissions.md) in a project
+can close merge requests in the project:
+
+1. Go to the merge request you want to close.
+1. Scroll to the comment box at the bottom of the page.
+1. Following the comment box, select **Close merge request**.
+
+GitLab closes the merge request, but preserves records of the merge request,
+its comments, and any associated pipelines.
+
+### Delete a merge request
+
+GitLab recommends you close, rather than delete, merge requests.
+
+WARNING:
+You cannot undo the deletion of a merge request.
+
+To delete a merge request:
+
+1. Sign in to GitLab as a user with the project Owner [role](../../permissions.md).
+   Only users with this role can delete merge requests in a project.
+1. Go to the merge request you want to delete, and select **Edit**.
+1. Scroll to the bottom of the page, and select **Delete merge request**.
+
 ## Merge request workflows
 
 For a software developer working in a team: