Readme should use new docker compose format instead of the old one

Signed-off-by: Callum Rogers <callumrogers@hotmail.co.uk>

README.md

@@ -22,14 +22,15 @@ they can be run together in an isolated environment:
 
 A `docker-compose.yml` looks like this:
 
+    version: '2'
+
+    services:
       web:
         build: .
         ports:
          - "5000:5000"
         volumes:
          - .:/code
-      links:
-       - redis
       redis:
         image: redis