Add Jenkins.

README.md

 * [Travis CI](https://travis-ci.org/) - A continuous integration platform.
 * [PHPCI](http://www.phptesting.org/) - An open source continuous integration platform for PHP.
 * [Sismo](http://sismo.sensiolabs.org/) - A continuous testing server library.
+* [Jenkins](http://jenkins-ci.org/) A continous integration platform with [PHP support](http://jenkins-php.org/index.html).
 
 ## Documentation
 *Libraries for generating project documentation.*