minimal trac/gitlab migration process (gitlab#21)

howto/trac.md

@@ -352,6 +352,19 @@ have to adjust our workflows to work around this. In some cases, we can use
 gitlab milestone pages or projects that do not need a wiki page as a work
 around.
 
+## Actual migration process
+
+The following repositories contain the source code that was used in
+the migration:
+
+ * <https://gitlab.torproject.org/ahf/gitlab-migration-tool>
+ * <https://gitlab.torproject.org/ahf/gitlab-migration-utilities>
+ * <https://gitlab.torproject.org/ahf/label-cleanup>
+ * <https://gitlab.torproject.org/ahf/trac-migration>
+
+The migration process was done by @ahf but was never clearly
+documented (see [issue 21](https://gitlab.torproject.org/tpo/tpa/gitlab/-/issues/21)).
+
 ## Trac Archival
 
 A copy of all Trac web pages were stored in the [Internet