Update README to include running linter

Author: NorbertLoh

frontend/peerprep/README.md

@@ -78,6 +78,13 @@ Make sure to deploy the output of `npm run build`
 │   └── server/    # Server-side code
 ```
 
+### Lint check
+To run the lint check:
+
+```bash
+npm run lint
+```
+
 ## Styling
 
 This template comes with [Tailwind CSS](https://tailwindcss.com/) already configured for a simple default starting experience. You can use whatever CSS framework you prefer.