Add documentation about "edit release" page

This commit adds some information about the new "Edit Release" page.

doc/user/project/releases/index.md

@@ -65,6 +65,27 @@ project.
 
 ![Releases list](img/releases.png)
 
+## Editing a release
+
+> [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/26016) in GitLab 12.5.
+
+To edit the details of a release, navigate to **Project overview > Releases** and click
+the edit button (pencil icon) in the top-right corner of the release you want to modify.
+
+![A release with an edit button](img/release_edit_button_v12_5.png)
+
+This will bring you to the **Edit Release** page, from which you can
+change some of the release's details.
+
+![Edit release page](img/edit_release_page_v12_5.png)
+
+Currently, it is only possible to edit the release title and notes.
+To change other release information, such as its tag, associated
+milestones, or release date, use the
+[Releases API](../../../api/releases/index.md#update-a-release). Editing this
+information through the **Edit Release** page is planned for a future version
+of GitLab.
+
 ## Notification for Releases
 
 > [Introduced](https://gitlab.com/gitlab-org/gitlab/issues/26001) in GitLab 12.4.