Only works for me with port 80 and 443 forwarded

For the docker client to work correctly I needed to forward both ports 443 and 80. I will take a closer look on how this is supposed to work.

docs/using.rst

@@ -73,7 +73,7 @@ to, `install Docker`_, then issue the following command:
 
 .. code-block:: shell
 
-   sudo docker run -it --rm -p 443:443 --name letsencrypt \
+   sudo docker run -it --rm -p 443:443 -p 80:80 --name letsencrypt \
                -v "/etc/letsencrypt:/etc/letsencrypt" \
                -v "/var/lib/letsencrypt:/var/lib/letsencrypt" \
                quay.io/letsencrypt/letsencrypt:latest auth