Merge pull request #1039 from gionn/patch-1

Fix docker run command in using.rst

docs/using.rst

@@ -76,7 +76,7 @@ server that the domain your requesting a cert for resolves to,
 
 .. code-block:: shell
 
-   sudo docker auth -it --rm -p 443:443 --name letsencrypt \
+   sudo docker run -it --rm -p 443:443 --name letsencrypt \
                -v "/etc/letsencrypt:/etc/letsencrypt" \
                -v "/var/lib/letsencrypt:/var/lib/letsencrypt" \
                quay.io/letsencrypt/letsencrypt:latest auth