Add a link to static files troubleshooting in the online docs

Author: rolandgeider

docker-compose.yml

@@ -121,6 +121,8 @@ volumes:
   # Heads up, if you remove these volumes and use folders directly you need to chown them
   # to the UID and GID 1000 even if it doesn't exist on your system. Also, they should
   # be readable by everyone.
+  #
+  # https://wger.readthedocs.io/en/latest/production/docker.html#missing-static-files
   media:
   static: