[10.x] Document FrankenPHP Docker install

[dunglas]

As discussed in laravel/octane#829 (comment).

This is largely inspired by https://chriswhite.is/coding/frankenphp-and-laravel-octane-with-docker/.

[taylorotwell]

@dunglas is this for production or local dev or both?

[dunglas]

@taylorotwell both, however, some improvements such as copying the prod php.ini (described in the linked page) can be done in production.