Add example for static names in README.md (nginx-proxy#257)

* Updates README.md

README.md

@@ -105,7 +105,24 @@ $ docker run -d \
 
 * Then start any containers to be proxied as described previously.
 
-Note: If the docker-gen container name is static and you want to explicitly set it, use `-e NGINX_DOCKER_GEN_CONTAINER=nginx-gen`. The same thing is true with the nginx container (`-e NGINX_PROXY_CONTAINER=nginx`).
+Note: 
+If the 3 containers are using static names, both labels `com.github.jrcs.letsencrypt_nginx_proxy_companion.nginx_proxy` on nginx container and `com.github.jrcs.letsencrypt_nginx_proxy_companion.docker_gen` on the docker-gen container can be removed. 
+
+The docker environment variables to be set on the letsencrypt container are:
+* `NGINX_DOCKER_GEN_CONTAINER` set to the name of the nginx container (here `nginx`)
+* `NGINX_PROXY_CONTAINER` set to the name of the docker-gen container (here `nginx-gen`)
+
+Example:
+```bash
+$ docker run -d \
+    --name nginx-letsencrypt \
+    --volumes-from nginx \
+    -v /path/to/certs:/etc/nginx/certs:rw \
+    -v /var/run/docker.sock:/var/run/docker.sock:ro \
+    -e NGINX_DOCKER_GEN_CONTAINER=nginx-gen \
+    -e NGINX_PROXY_CONTAINER=nginx \
+    jrcs/letsencrypt-nginx-proxy-companion
+```
 
 
 #### Let's Encrypt