ADD env variables to db container

FIX Error: Database is uninitialized and superuser password is not specified.
Env vars needs to be defined in both the "db" and "web" containers 
In "db", so it can create the default user from it
In "web", so it can be used in settings.py to connect django to the postgres container

samples/django.md

@@ -75,6 +75,10 @@ and a `docker-compose.yml` file. (You can use either a `.yml` or `.yaml` extensi
        image: postgres
        volumes:
          - ./data/db:/var/lib/postgresql/data
+       environment:
+         - POSTGRES_NAME=postgres
+         - POSTGRES_USER=postgres
+         - POSTGRES_PASSWORD=postgres
      web:
        build: .
        command: python manage.py runserver 0.0.0.0:8000