Add docker compose example to README.md (#1085)

* Add docker compose example to README.md

`docker-compose` is standard, and following `linuxserver`'s excellent example, including it in the README.md enables a far more efficient quick start.

* Add cap-add and fix driver definition

* Fix config

* cap-add -> cap_add

README.md

@@ -27,6 +27,33 @@ $ docker run --cap-add=NET_ADMIN -d \
               haugene/transmission-openvpn
 ```
 
+## Docker Compose
+```
+version: '3.3'
+services:
+    transmission-openvpn:
+        volumes:
+            - '/your/storage/path/:/data'
+            - '/etc/localtime:/etc/localtime:ro'
+        environment:
+            - CREATE_TUN_DEVICE=true
+            - OPENVPN_PROVIDER=PIA
+            - OPENVPN_CONFIG=CA Toronto
+            - OPENVPN_USERNAME=user
+            - OPENVPN_PASSWORD=pass
+            - WEBPROXY_ENABLED=false
+            - LOCAL_NETWORK=192.168.0.0/16
+        cap_add:
+            - NET_ADMIN
+        logging:
+            driver: json-file
+            options:
+                max-size: 10m
+        ports:
+            - '9091:9091'
+        image: haugene/transmission-openvpn
+```
+
 ## Documentation
 The full documentation is available at https://haugene.github.io/docker-transmission-openvpn/.