Add CakePHP to list of frameworks

README.md

 * [Laravel 4](http://laravel.com/) - A simple PHP framework.
 * [Aura PHP](http://auraphp.com/) - A framework of independent components.
 * [Phalcon](http://phalconphp.com/en/) - A framework implemented as a C extension.
+* [CakePHP](http://cakephp.org/) - A rapid application development framework.
 
 ## Framework Extras
 *Extras related to web development frameworks.*