This is a somewhat standalone entrypoint you could use to start testing your website.
You could also take the contents of the composer.json file and add them to your devDependencies in your own composer.json file (and move the behat.yml and its files appropriately).
Be careful - this would end up running against a 'live' site so do not use it on production!
This is set up to work with headless chrome. To do so, you need to know the path to chrome:
/path/to/chrome --disable-gpu --headless --remote-debugging-address=0.0.0.0 --remote-debugging-port=9222
So on OSX, it will likely be:
/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --disable-gpu --headless --remote-debugging-address=0.0.0.0 --remote-debugging-port=9222