Adding docker entry for backend

This allow you to run `docker-compose up` in the backend directory
to run the whole backend in a docker. by default the port is set to 4000

backend/compose.yaml

@@ -1,4 +1,8 @@
 services:
+  backend:
+    build: .
+    ports:
+      - 4000:8080
   postgres:
     image: 'postgres:latest'
     environment: