create a Laravel demo app

https://github.com/Astrotomic/stancy-laravel-demo

The demo app should show the basic features and in best case contain some integration tests using [spatie/phpunit-snapshot-assertions](https://github.com/spatie/phpunit-snapshot-assertions). Only simple tests like: if I call this url/route I expect this response/html/snapshot.

relates to #8

Start with the linked stancy-laravel-demo repository and review the package's basic features to determine what the demo should cover. Use the requested simple URL or route checks with spatie/phpunit-snapshot-assertions where appropriate. Done means the demo app exists, shows the basic features, and includes the described integration tests.

Written by the indexing model from the issue text.