docs(README.md): add npm version badge [ci skip]

Author: jedwards1211

README.md

@@ -4,6 +4,7 @@
 [![Coverage Status](https://codecov.io/gh/jedwards1211/es2015-library-skeleton/branch/master/graph/badge.svg)](https://codecov.io/gh/jedwards1211/es2015-library-skeleton)
 [![semantic-release](https://img.shields.io/badge/%20%20%F0%9F%93%A6%F0%9F%9A%80-semantic--release-e10079.svg)](https://github.com/semantic-release/semantic-release)
 [![Commitizen friendly](https://img.shields.io/badge/commitizen-friendly-brightgreen.svg)](http://commitizen.github.io/cz-cli/)
+[![npm version](https://badge.fury.io/js/es2015-library-skeleton.svg)](https://badge.fury.io/js/es2015-library-skeleton)
 
 This is my personal skeleton for creating an ES2015 library npm package.  You are welcome to use it.