📝 Add `Enabling Open User Registration` to backend docs (#1191)

backend/README.md

@@ -63,6 +63,16 @@ Make sure your editor is using the correct Python virtual environment.
 
 Modify or add SQLModel models for data and SQL tables in `./backend/app/models.py`, API endpoints in `./backend/app/api/`, CRUD (Create, Read, Update, Delete) utils in `./backend/app/crud.py`.
 
+### Enabling Open User Registration
+
+By default the backend has user registration disabled, but there's already a route to register users. If you want to allow users to register themselves, you can set the environment variable `USERS_OPEN_REGISTRATION` to `True` in the `.env` file.
+
+After modifying the environment variables, restart the Docker containers to apply the changes. You can do this by running:
+
+```console
+$ docker compose up -d
+```
+
 ### VS Code
 
 There are already configurations in place to run the backend through the VS Code debugger, so that you can use breakpoints, pause and explore variables, etc.