Update Docker Compose file format 3

compose/demo/django/docker-compose.yml

@@ -0,0 +1,15 @@
+version: "3"
+services:
+
+  db:
+    image: postgres
+
+  web:
+    build: .
+    command: python3 manage.py runserver 0.0.0.0:8000
+    volumes:
+      - .:/code
+    ports:
+      - "8000:8000"
+    links:
+      - db