Update README.md

Author: mreram

README.md

@@ -1,4 +1,6 @@
 # ShowCaseView
+[![Android Arsenal](https://img.shields.io/badge/Android%20Arsenal-FlatShowCaseView-brightgreen.svg?style=flat)](https://android-arsenal.com/details/1/6713)
+
 <p align="center">
 <img src="./screenshots/Screenshot_2018-01-21-00-51-52.png" width="200"/>
 <img src="./screenshots/Screenshot_2018-01-21-00-52-43.png" width="200"/>