Add big warning to compose file

docker/docker-compose.yml

@@ -1,5 +1,9 @@
 version: "3.4"
 
+# DO NOT USE THIS IN PRODUCTION - it is for development only due to insecure
+# settings and the use of "runserver" versus "gunicorn".
+# See https://takahe-server.readthedocs.io/en/latest/installation.html for more
+
 x-takahe-common:
   &takahe-common
     build: .