Update 'README.md'

README.md

@@ -40,6 +40,8 @@ restart. You don't need to modify ``config.php`` manually for this.
 accessible on the net, without using a reverse proxy sharing same host, you will need to
 remove ``127.0.0.1:`` from ``HTTP_PORT`` variable in ``.env``.
 
+* Please don't rename the services inside `docker-compose.yml` unless you know what you're doing. Web container expects application container to be named `app`, if you rename it and it's not accessible via Docker DNS as `http://app` you will run into 502 errors on startup.
+
 #### Build and start the container
 
 ```sh