Add Code Quality tool.

README.md

 ### Code Quality
 *Libraries for managing code quality, formatting and linting.*
 
+* [CaptainHook](https://github.com/captainhookphp/captainhook) - An easy-to-use and flexible Git hook library. 
 * [PHP CodeSniffer](https://github.com/squizlabs/PHP_CodeSniffer) - A library that detects PHP, CSS and JS coding standard violations.
 * [PHP CS Fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer) - A coding standards fixer library.
 * [PHP Mess Detector](https://github.com/phpmd/phpmd) - A library that scans code for bugs, sub-optimal code, unused parameters and more.