Add tests badge in README

[ci-skip]

Author: joanhey

README.md

@@ -1,5 +1,5 @@
 # PHP Frameworks Bench
-![GitHub release (latest by date)](https://img.shields.io/github/v/release/myaaghubi/PHP-Frameworks-Bench?color=purpol) ![GitHub](https://img.shields.io/github/license/myaaghubi/PHP-Frameworks-Bench?color=green)
+[![Test PHP benchmark](https://github.com/myaaghubi/PHP-Frameworks-Bench/actions/workflows/test.yml/badge.svg)](https://github.com/myaaghubi/PHP-Frameworks-Bench/actions/workflows/test.yml) ![GitHub release (latest by date)](https://img.shields.io/github/v/release/myaaghubi/PHP-Frameworks-Bench?color=purpol) ![GitHub](https://img.shields.io/github/license/myaaghubi/PHP-Frameworks-Bench?color=green)
 
 This project attempts to measure the minimum overhead (minimum bootstrap cost) of PHP frameworks in the real world.