Added PHPCheckstyle

README.md

 * [PHPLOC](https://github.com/sebastianbergmann/phploc) - A tool for quickly measuring the size of a PHP project.
 * [xDebug](https://github.com/xdebug/xdebug) - A debug and profile tool for PHP.
 * [xHprof](https://github.com/phacility/xhprof) - Another profiling tool for PHP.
+* [PHPCheckstyle](https://github.com/jbrooksuk/phpcheckstyle) - A tool to help adhere to certain coding conventions.
 
 ## Build Tools
 *Project build and automation tools.*