Document backup pipeline behaviour

systemd/zorruno-docker-backup-mqtt.service

@@ -5,6 +5,8 @@ Wants=network-online.target
 
 [Service]
 Type=simple
+# Root is required because the listener launches a pipeline that stops and
+# starts Docker Compose projects and reads all project data.
 User=root
 WorkingDirectory=/backupdockerscripts
 ExecStart=/backupdockerscripts/bin/mqtt-trigger-listener.sh