Require .env file for docker compose example

docker-compose.yml

@@ -6,6 +6,9 @@ services:
       - 127.0.0.1:8000:8000
     mem_limit: '256m'
     user: "${UID}:${GID}" # if you run into issues with permissions for the data-files volume below, see other options at https://stackoverflow.com/a/56904335
+    env_file:
+      - path: .env
+        required: true
     volumes:
       - ./data-files:/app/data-files