service/documentation.md

@@ -4,6 +4,10 @@ and possibly other documentation systems inside TPO.
 Note that there is a different service called [status](service/status)
 for the status page at <https://status.torproject.org>.
 
+There's also a guide specifically aimed at aiding people write
+user-facing documentation in the [Tor User Documentation Style
+Guide](https://gitlab.torproject.org/tpo/team/-/wikis/Tor-User-Documentation-Style-Guide).
+
 > The palest ink is better than the most capricious memory.
 >
 > -- ancient Chinese proverb