docs(README): add npm badge

Author: pine

README.md

@@ -1,6 +1,8 @@
 ArrayBuffer loader for webpack
 ------------------------------
 
+[![NPM](https://nodei.co/npm/arraybuffer-loader.png?downloads=true&downloadRank=true&stars=true)](https://nodei.co/npm/arraybuffer-loader/)
+
 [![npm](https://img.shields.io/npm/v/arraybuffer-loader.svg?maxAge=2592000&style=flat-square)](https://www.npmjs.org/package/arraybuffer-loader)
 [![Travis](https://img.shields.io/travis/pine/arraybuffer-loader/master.svg?maxAge=2592000&style=flat-square)](https://travis-ci.org/pine/arraybuffer-loader)
 [![Build Status](https://img.shields.io/appveyor/ci/pine/arraybuffer-loader/master.svg?style=flat-square&maxAge=2592000)](https://ci.appveyor.com/project/pine/arraybuffer-loader/branch/master)