docs: add localhost testing instructions to README

Co-authored-by: aider (openrouter/thinkingmachines/inkling-small:free) <aider@aider.chat>

README.md

@@ -1,3 +1,15 @@
 # golf-score
 
-Single page score card and stats app
+Single page score card and stats app
+
+## Testing on localhost
+
+1. Install dependencies:
+   pip install fastapi uvicorn sqlalchemy pydantic
+
+2. Start the backend:
+   uvicorn backend.app:app --reload
+
+3. Open http://localhost:8000/ in your browser.
+
+The SQLite database (backend/golf.db) is created automatically with a mock course.