Update README.md

Author: barryvdh

README.md

@@ -1,6 +1,7 @@
 # Stack/Cors
 
 [![Unit Tests](https://github.com/fruitcake/php-cors/actions/workflows/run-tests.yml/badge.svg)](https://github.com/fruitcake/php-cors/actions)
+[![PHPStan Level 9](https://img.shields.io/badge/PHPStan-Level%209-blue)](https://github.com/fruitcake/php-cors/actions)
 [![Packagist License](https://poser.pugx.org/fruitcake/php-cors/license.png)](http://choosealicense.com/licenses/mit/)
 [![Latest Stable Version](https://poser.pugx.org/fruitcake/php-cors/version.png)](https://packagist.org/packages/fruitcake/php-cors)
 [![Total Downloads](https://poser.pugx.org/fruitcake/php-cors/d/total.png)](https://packagist.org/packages/fruitcake/php-cors)
@@ -73,4 +74,4 @@ $cors->isPreflightRequest(Request $request);
 
 Released under the MIT License, see [LICENSE](LICENSE).
 The original author of this Library is Alexander <iam.asm89@gmail.com>, while Barry <barryvdh@gmail.com> has been involved since 2015.
-This package is split-off from https://github.com/asm89/stack-cors
+This package is split-off from https://github.com/asm89/stack-cors