howto/rename-a-host: add ud-ldap fix

howto/rename-a-host.md

@@ -30,6 +30,12 @@ Then adjust the SSH host keys. Generating new keys isn't mandatory:
 
     sed -i 's/foo/bar/' /etc/ssh/ssh_host_*.pub
 
+We also need to fix the `thishost` symlink in ud-ldap data:
+
+    ud-replicate
+    cd /var/lib/misc && ln -sf bar.torproject.org thishost
+    rm -rf foo.torproject.org
+
 ## Rename the machine in the infrastructure
 
 ### Ganeti