The original blog post can be found here: http://blog.brunoscopelliti.com/building-a-restful-service-with-angularjs-and-php-backend-setup. I've tried to keep the logic the same as the original post.
Write a composer.json, and require Silex. If you don't know about composer, you can learn about it at getcomposer.org. It's a package manager for PHP like NPM for node, most major projects now use this for managing dependencies.
{