A doc page to list everything you can do with Playground

Topics to cover:

* https://github.com/WordPress/wordpress-playground/issues/1074
* https://github.com/WordPress/blueprints/issues/64
* Development environments (wp now, VS Code)
* WordPress extensions ([WordPress Playground plugin](https://github.com/WordPress/playground-tools/releases/tag/v0.1.65), [WordPress Playground block](https://wordpress.org/plugins/interactive-code-block/))
