Update docs for VIRTUAL_PORT

README.md

@@ -2,6 +2,8 @@ nginx-proxy sets up a container running nginx and [docker-gen][1].  docker-gen g
 
 See [Automated Nginx Reverse Proxy for Docker][2] for why you might want to use this.
 
+### Usage
+
 To run it:
 
     $ docker run -d -p 80:80 -v /var/run/docker.sock:/tmp/docker.sock -t jwilder/nginx-proxy
@@ -39,6 +41,9 @@ Provided your DNS is setup to forward foo.bar.com to the a host running nginx-pr
 
     CMD ["/usr/bin/supervisord"]
 
+### Multiple Ports
+
+If your container exposes multiple ports, nginx-proxy will default to the service running on port 80.  If you need to specify a different port, you can set a VIRTUAL_PORT env var to select a different one.  If your container only exposes one port and it has a VIRTUAL_HOST env var set, that port will be selected.
 
   [1]: https://github.com/jwilder/docker-gen
   [2]: http://jasonwilder.com/blog/2014/03/25/automated-nginx-reverse-proxy-for-docker/