Add CI badge

Author: Slamdunk

README.md

@@ -3,6 +3,7 @@
 DeepCopy helps you create deep copies (clones) of your objects. It is designed to handle cycles in the association graph.
 
 [![Total Downloads](https://poser.pugx.org/myclabs/deep-copy/downloads.svg)](https://packagist.org/packages/myclabs/deep-copy)
+[![Integrate](https://github.com/myclabs/DeepCopy/workflows/ci/badge.svg?branch=1.x)](https://github.com/myclabs/DeepCopy/actions)
 
 ## Table of Contents