Add a GitPOAP badge in the readme (#2594)

Author: katspaugh

README.md

@@ -2,6 +2,7 @@
 
 [![npm version](https://img.shields.io/npm/v/wavesurfer.js.svg?style=flat)](https://www.npmjs.com/package/wavesurfer.js)
 ![npm](https://img.shields.io/npm/dm/wavesurfer.js.svg) [![Join the chat at https://gitter.im/katspaugh/wavesurfer.js](https://badges.gitter.im/katspaugh/wavesurfer.js.svg)](https://gitter.im/katspaugh/wavesurfer.js?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+[![GitPOAP Badge](https://public-api.gitpoap.io/v1/repo/katspaugh/wavesurfer.js/badge)](https://www.gitpoap.io/gh/katspaugh/wavesurfer.js)
 
 Interactive navigable audio visualization using Web Audio and Canvas.