fix authentication issue in wiki replica instructions

Seems like this may fix team#40376

howto/gitlab.md

@@ -440,13 +440,22 @@ into a separate project.
 
      * Git repository URL: the HTTPS URL of the Git repository (which
        you can find in the **Clone repository** page on the top-right
-       of the wiki)
+       of the wiki) **Important**: Make sure you add a *username* to
+       the HTTPS URL, otherwise mirroring will fail. For example, this
+       wiki URL:
+         
+            https://gitlab.torproject.org/tpo/tpa/team.wiki.git
+        
+         should actually be:
+         
+            https://wiki-replica@gitlab.torproject.org/tpo/tpa/team.wiki.git
+
      * **Mirror direction**: `push` (only "free" option, `pull` is
        non-free)
      * **Authentication method**: `Password` (default)
      * **Password**: the **Access token** you created in the first
        step
-     * **Keep divergent refs**: checked (optional, should make sure
+     * **Keep divergent refs**: unchecked (optional, should make sure
        sync works in some edge cases)
      * **Mirror only protected branches**: checked (to keep merge
        requests from being needlessly mirrored to the wiki)