Add log command to logging article

docs/firststeps-logging.md

@@ -1,6 +1,7 @@
 Logging in mailcow: dockerized consists of multiple stages, but is, after all, much more flexible and easier to integrate into a logging daemon than before.
 
 In Docker the containerized application (PID 1) writes its output to stdout. For real one-application containers this works just fine.
+Run `docker-compose logs --help` to learn more. 
 
 Some containers log or stream to multiple destinations.