Updated FAQ (markdown)

FAQ.md

@@ -7,6 +7,35 @@ You'll probably want to `push` your config updates to your server and restart th
 Mails are stored in `/var/mail/${domain}/${username}`.  
 You should use a [data volume container](https://medium.com/@ramangupta/why-docker-data-containers-are-good-589b3c6c749e#.uxyrp7xpu) for `/var/mail` for data persistence. Otherwise, your data may be lost.
 
+### How can I use data volume container as proposed above?
+
+Here is a `docker-compose.yml` example which use a data volume container for email storage named `maildata`.
+
+    maildata:
+      image: ubuntu
+      volumes:
+        - /var/mail
+      command: /bin/true
+
+    mail:
+      image: "tvial/docker-mailserver"
+      hostname: "mail"
+      domainname: "domain.com"
+      volumes_from:
+       - maildata
+      ports:
+      - "25:25"
+      - "143:143"
+      - "587:587"
+      - "993:993"
+      volumes:
+      - ./spamassassin:/tmp/spamassassin/
+      - ./postfix:/tmp/postfix/
+      - ./opendkim/keys:/etc/opendkim/keys
+      - ./letsencrypt/etc:/etc/letsencrypt
+      environment:
+      - DMS_SSL=letsencrypt
+
 ### What about backups?
 
 Assuming that you use `docker-compose` and a data volume container named `maildata`, you can backup your user mails like this: