[Docs] Missing reference to playwright-cli on https://playwright.dev

[erosenberg]

These pages exist currently on the docs site:

• https://playwright.dev/docs/test-cli
• https://playwright.dev/docs/test-agents

Can we get a separate page with a reference to this tool? Can we also get a quick summary on that page of the differences between the usage of the tools above? It's causing a solid amount of confusion on my team. This project is awesome and can't wait to use it more!