Added docker-compose.yml example file.

docker-compose.yml

@@ -0,0 +1,20 @@
+mail:
+  # image: tvial/docker-mailserver
+  build: .
+  hostname: mail
+  domainname: my-domain.com
+  ports:
+  - "25:25"
+  - "143:143"
+  - "587:587"
+  - "993:993"
+  environment:
+    docker_mail_domain: "my-domain.com"
+    # format is user@domain.tld|clear_password
+    docker_mail_users:
+      - "username1@my-domain.com|username1password"
+      - "username2@my-domain.com|username2password"
+    # format is user@domain.tld|list,of,aliases,comma,separated
+    docker_mail_aliases:
+      - "username1@my-domain.com|alias1,alias2,alias3"
+      - "username2@my-domain.com|alias4"