Move compose settings to env file

README.md

@@ -38,7 +38,7 @@ source .venv/bin/activate
 pip install -e ".[dev]"
 ```
 
-### Run
+### Run Container
 
 ```bash
 export FLASK_APP=wsgi.py
@@ -86,6 +86,12 @@ Open `http://127.0.0.1:8000`.
 docker compose up --build web
 ```
 
+Compose settings are stored in `env`. Update that file to change values such as:
+
+- `SECRET_KEY`
+- `MAX_UPLOAD_SIZE_MB`
+- `OUTPUT_DIRECTORY`
+
 ### Run the test suite in a container
 
 ```bash