Add details on starting/stopping the broker from the snap

Closes #3197. Thanks to Van Phat Phan.

www/pages/documentation/using-the-snap.md

@@ -74,6 +74,20 @@ and keys, must also be placed in `/var/snap/mosquitto/common/` - in new folders
 if wanted. This directory is the only place accessible by Mosquitto when
 running as a snap.
 
+Starting and stopping the broker service can be done with the snap command:
+
+```
+snap start mosquitto
+snap stop mosquitto
+```
+
+Or via systemd:
+
+```
+systemctl start snap.mosquitto.mosquitto
+systemctl stop snap.mosquitto.mosquitto
+```
+
 All other aspects of running Mosquitto are the same as with any other
 installation methods.