Add docker letsencrypt example

Configure-SSL.md

@@ -17,6 +17,28 @@ To enable Let's Encrypt on your mail server, you have to:
 
 You don't have anything else to do. Enjoy.
 
+#### Example using docker for letsencrypt
+Make a directory to store your letsencrypt logs and configs.
+
+In my case
+```
+mkdir -p /home/ubuntu/docker/letsencrypt/log 
+mkdir -p /home/ubuntu/docker/letsencrypt/etc/letsencrypt
+```
+
+Now get the certificate (modify ```mail.myserver.tld```) and following the certbot instructions.
+This will need access to port 443 from the internet, adjust your firewall if needed
+```
+docker run --rm -ti -v $PWD/log/:/var/log/letsencrypt/ -v $PWD/etc/:/etc/letsencrypt/ -p 443:443 deliverous/certbot certonly --standalone -d mail.myserver.tld
+```
+You can now mount /home/ubuntu/docker/letsencrypt/etc/letsencrypt in /etc/letsencrypt of ```docker-mailserver```
+
+To renew your certificate just run (this will need access to port 443 from the internet, adjust your firewall if needed)
+```
+docker run --rm -ti -v $PWD/log/:/var/log/letsencrypt/ -v $PWD/etc/:/etc/letsencrypt/ -p 443:443 deliverous/certbot renew
+```
+
+
 ### Self-signed certificates (testing only)
 
 You can easily generate a self-signed SSL certificate by using the following command: