adding npm badge (#9)

README.md

@@ -3,7 +3,7 @@
 A scheduler based on [`requestAnimationFrame`](https://developer.mozilla.org/en-US/docs/Web/API/window/requestAnimationFrame). It throttles calls to a function and only invokes it with the latest argument in the frame period.
 
 
-[![Build Status](https://travis-ci.org/alexreardon/raf-schd.svg?branch=master)](https://travis-ci.org/alexreardon/raf-schd) [![dependencies](https://david-dm.org/alexreardon/raf-schd.svg)](https://david-dm.org/alexreardon/raf-schd) [![SemVer](https://img.shields.io/badge/SemVer-2.0.0-brightgreen.svg)](http://semver.org/spec/v2.0.0.html)
+[![Build Status](https://travis-ci.org/alexreardon/raf-schd.svg?branch=master)](https://travis-ci.org/alexreardon/raf-schd) [![dependencies](https://david-dm.org/alexreardon/raf-schd.svg)](https://david-dm.org/alexreardon/raf-schd) [![npm](https://img.shields.io/npm/v/raf-schd.svg)](https://www.npmjs.com/package/raf-schd) [![SemVer](https://img.shields.io/badge/SemVer-2.0.0-brightgreen.svg)](http://semver.org/spec/v2.0.0.html)
 
 
 ```js