Update doc

README.md

@@ -67,16 +67,26 @@ You can activate the IPv6 support for the nginx-proxy container by passing the v
 
     $ docker run -d -p 80:80 -e ENABLE_IPV6=true -v /var/run/docker.sock:/tmp/docker.sock:ro pinidh/nginx-proxy
 
-### Multiple Ports
+### Multiple Hosts
 
-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.
+If you need to support multiple virtual hosts for a container, you can separate each entry with commas.  For example, `foo.bar.com,baz.bar.com,bar.com` and each host will be setup the same.
 
-  [1]: https://github.com/jwilder/docker-gen
-  [2]: http://jasonwilder.com/blog/2014/03/25/automated-nginx-reverse-proxy-for-docker/
+### Virtual Ports
 
-### Multiple Hosts
+When your container exposes only one port, nginx-proxy will default to this port, else to port 80.
 
-If you need to support multiple virtual hosts for a container, you can separate each entry with commas.  For example, `foo.bar.com,baz.bar.com,bar.com` and each host will be setup the same.
+If you need to specify a different port, you can set a `VIRTUAL_PORT` env var to select a different one. This variable cannot be set to more than one port.
+
+If you need to specify a different port for each virtual host, use this syntax for the `VIRTUAL_HOST` variable:
+```
+VIRTUAL_HOST=host1:port1,host2:port2,...
+```
+
+For each host defined into `VIRTUAL_HOST`, the associated virtual port is retrieved by order of precedence:
+1. From the `host:port` syntax in the `VIRTUAL_HOST` definition
+1. From the `VIRTUAL_PORT` environment variable
+1. From the container's exposed port if there is only one
+1. From the default port 80 when none of the above methods apply
 
 ### Wildcard Hosts