Add doc for local config with .env (#138)

CONTRIBUTING.md

@@ -77,6 +77,24 @@ poetry run python
 poetry run datadoc
 ```
 
+## Config for local development
+
+We use a python package called `python-dotenv` for configuration management. This gives two possibilities for sourcing configuration:
+
+1. Environment variables.
+1. A file called `.env` by convention.
+
+To set up for local development run this command from the root of the repo.
+
+1. Create a file `src/datadoc/.env`
+1. Place the following lines in the file:
+```
+DATADOC_DASH_DEVELOPMENT_MODE=True
+DATADOC_LOG_LEVEL=debug
+```
+
+To see all configuration options, see `src/datadoc/config.py`
+
 ## How to test the project
 
 Run the full test suite:

src/datadoc/app.py

@@ -118,7 +118,9 @@ def main(dataset_path: str | None = None) -> None:
             port=port,
         )
     else:
-        app.run(debug=config.get_dash_development_mode(), port=port)
+        if dev_mode := config.get_dash_development_mode():
+            logger.warning("Starting in Development Mode. NOT SUITABLE FOR PRODUCTION.")
+        app.run(debug=dev_mode, port=port)
 
 
 if __name__ == "__main__":