feat: Update maintenance how to

To add command to visualize tasks list

doc/how-to-guides/deployment/maintenance.md

@@ -34,6 +34,8 @@ Take the time to become a bit familiar with docker-compose if it's your first us
 
 ## Monitor
 
+### See logs
+
 To display the logs of the container, `docker compose logs [service-name]`.
 (without service-name, you got all logs).
 
@@ -53,6 +55,19 @@ robotoff_worker_high_1     /bin/sh -c /docker-entrypo ...   Up
 ...                              
 ```
 
+### See number of tasks in queues
+
+If you want to monitor how much job robotoff has to do (how behind it is),
+you can run the `rq` command to get status:
+
+```bash
+docker compose run --rm --no-deps worker_1 rq info
+```
+
+This may help you understand why robotoff insight are not visible immediately on products.
+
+See also [rq monitoring documentation](https://python-rq.org/docs/monitoring/) for more commands and informations.
+
 ## Database backup and restore
 
 To backup the PostgreSQL database, run the following command:
@@ -68,4 +83,4 @@ You can restore it easily by copying the dump file inside the container and laun
 ```bash
 docker cp -a robotoff_postgres.dump robotoff_postgres_1:/tmp/
 docker exec -it robotoff_postgres_1 pg_restore -v -d postgres -U postgres -j 8 --if-exists /tmp/robotoff_postgres.dump
-```
+```