add npm badge in readme

Author: albincorreya

README.md

@@ -2,6 +2,7 @@
 ![alt text](https://user-images.githubusercontent.com/14850001/66190489-67098d80-e68c-11e9-9a7c-35b82f6635e1.png)
 
 [![Build Status](https://travis-ci.org/MTG/essentia.js.svg?branch=master)](https://travis-ci.org/MTG/essentia.js)
+[![npm version](https://badge.fury.io/js/essentia.js.svg)](https://badge.fury.io/js/essentia.js)
 [![License: AGPL v3](https://img.shields.io/badge/License-AGPL%20v3-blue.svg)](https://www.gnu.org/licenses/agpl-3.0)
 
 JavaScript port and bindings for [essentia C++ music/audio analysis library](https://essentia.upf.edu) using [Emscripten](https://emscripten.org/) toolchain and [WebAssembly](https://webassembly.org/). Currently, essentia.js builds only support essentia standard mode algorithms besides the ones that are listed [here](src/python/excluded_algos.md). [essentia.js](https://essentia.upf.edu/essentiajs) enables state-of-the-art audio/music analysis algorithms on your web-client and nodejs applications.