Add PHPCI (suggestion by @Kristories).

README.md

 * [VFS Stream](https://github.com/mikey179/vfsStream) - A virtual filesystem stream wrapper for testing.
 * [Locust](http://locust.io/) - A modern load test library written in Python.
 * [Travis CI](https://travis-ci.org/) - A continuous integration platform.
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+* [PHPCI](http://www.phptesting.org/) - An open source continuous integration platform for PHP.
 
 ## Documentation
 *Libraries for generating project documentation.*