service/documentation.md

@@ -405,6 +405,13 @@ or:
 If you can't find the GitLab documentation in the wiki, you can try to
 read the [latest copy in the wayback machine](https://web.archive.org/web/2/https://gitlab.torproject.org/tpo/tpa/team/-/wikis/howto/gitlab/).
 
+If GitLab is down for an extended period of time and you still want to
+collaborate over documentation, push the above git repository to
+another mirror, for example on [`gitlab.com`](https://gitlab.com). Here are the
+currently known mirrors of the TPA wiki:
+
+ - [anarcat](https://gitlab.com/anarcat/tpa-wiki-replica)
+
 ## Disaster recovery
 
 If GitLab disappears in a flaming ball of fire, it should be possible