docs: add development instructions to README

README.md

@@ -20,6 +20,18 @@ https://gitea.reversed.dev/space/time-until/releases
 - Shared UI components are in `src/components`.
 - Theme + styling are managed via `src/theme.js` and `src/styles.js`.
 
+## Development
+
+1. Install dependencies:
+   ```bash
+   npm install
+   ```
+
+2. Start the development server:
+   ```bash
+   npx expo start
+   ```
+
 ### Time Until Mode
 
 - Enter hour/minute in 24-hour format.