container works, update README, adding warning

mattermost-cleaner/README.md

-# postgres-backup
+# mattermost-cleaner
 
-This image delete automatic messages from Mattermost teams
-(previous version, only run on "nx1718").
+This image runs a cron to delete automatic messages from Mattermost teams (alpha version, only run on one team).
+Delete command is run once when container starts and then every hour (depending on parameter) via cron.
+
+**Warning** The commande delete directly data from database, which is bad pratice
+https://docs.mattermost.com/install/troubleshooting.html#important-notes
+https://docs.mattermost.com/deployment/on-boarding.html#do-not-manipulate-the-mattermost-database
 
-Delete command is run first when container starts and then every hour.
 
 ## Usage:
 
@@ -21,3 +24,19 @@ Delete command is run first when container starts and then every hour.
     POSTGRES_USER      the username of your postgres database
     POSTGRES_PASS      the password of your postgres database
     CRON_TIME       the interval of cron job to run postgresdump. `0 * * * *` by default, which is every hour
+
+## Docker-compose
+
+  mattermost-cleaner:
+    image: registry.picasoft.net:5000/mattermost-cleaner:alpha
+    container_name: mattermost-cleaner
+    links:
+      - mattermost-db:mattermost-db
+    environment:
+      - POSTGRES_HOST=mattermost-db
+      - POSTGRES_PORT=5432
+      - POSTGRES_USER=mattermost
+      - POSTGRES_PASS=...
+      - POSTGRES_DB=mattermost
+      - MATTERMOST_TEAM=name
+