docs: README missing instructions for running tests

[tomkis]

Summary

The README currently only documents how to install dependencies and start the development server, but does not mention how to run the test suite.

Current README

npm install
npm start
open http://localhost:3000

What's missing

The project has a test script defined in package.json that uses Jest, but this is not documented anywhere in the README. Contributors and users have no way of knowing they can run:

npm test

Proposed change

Add a section to the README explaining how to run the tests, for example:

npm test

This would help contributors verify their changes before submitting pull requests and generally improve the developer experience.