README: add link to changelog in badges

Author: jrfnl

README.md

@@ -5,6 +5,7 @@ PHPCSDevTools for developers of PHP_CodeSniffer sniffs
 
 [![Latest Stable Version](https://poser.pugx.org/phpcsstandards/phpcsdevtools/v/stable)](https://packagist.org/packages/phpcsstandards/phpcsdevtools)
 [![Release Date of the Latest Version](https://img.shields.io/github/release-date/PHPCSStandards/PHPCSDevTools.svg?maxAge=1800)](https://github.com/PHPCSStandards/PHPCSDevTools/releases)
+[![Changelog](https://img.shields.io/github/v/release/PHPCSStandards/PHPCSDevTools?label=Changelog&sort=semver)](https://github.com/PHPCSStandards/PHPCSDevTools/blob/stable/CHANGELOG.md)
 :construction:
 [![Latest Unstable Version](https://img.shields.io/badge/unstable-dev--develop-e68718.svg?maxAge=2419200)](https://packagist.org/packages/phpcsstandards/phpcsdevtools#dev-develop)
 [![Last Commit to Unstable](https://img.shields.io/github/last-commit/PHPCSStandards/PHPCSDevTools/develop.svg)](https://github.com/PHPCSStandards/PHPCSDevTools/commits/develop)