Document lingering, important detail

Author: tvlooy

messenger.rst

@@ -709,6 +709,14 @@ Restart all your consumers:
 
     $ systemctl --user restart messenger-consume@*.service
 
+The systemd user instance is only started after the first login of the
+particular user. We want to start our workers on system boot instead. Enable
+lingering on the user to activate that behavior:
+
+.. code-block:: terminal
+
+    $ loginctl enable-linger <your-username>
+
 Logs are managed by journald and can be worked with using the journalctl
 command, but you do need elevated privileges (sudo) for that: