Document use with playwright-test

[rattrayalex]

jest-playwright is now telling people to just use @playwright/test instead of Jest, eg:

import { test, expect } from '@playwright/test';

test.describe('headed block', () => {
  test.use({ headless: false });

  test('my headed test', async ({ page }) => {
    // ...
  });
});

$ npx playwright test

Currently there don't seem to be docs or examples on how to use root-cause with this test runner.