Add Codacy badge

Author: bkrem

README.md

@@ -1,6 +1,7 @@
 # React D3 Tree
 [![Build Status](https://travis-ci.org/bkrem/react-d3-tree.svg?branch=master)](https://travis-ci.org/bkrem/react-d3-tree)
 [![Coverage Status](https://coveralls.io/repos/github/bkrem/react-d3-tree/badge.svg?branch=master)](https://coveralls.io/github/bkrem/react-d3-tree?branch=master)
+[![Codacy Badge](https://api.codacy.com/project/badge/Grade/f9ed4796ee9c448dbcd80af2954cc0d1)](https://www.codacy.com/app/ben.kremer/react-d3-tree?utm_source=github.com&utm_medium=referral&utm_content=bkrem/react-d3-tree&utm_campaign=Badge_Grade)
 [![npm version](https://badge.fury.io/js/react-d3-tree.svg)](https://badge.fury.io/js/react-d3-tree)
 
 React D3 Tree is a [React](http://facebook.github.io/react/) component that lets you represent hierarchical data (e.g. ancestor trees, organisational structure, package dependencies) as an animated & interactive tree graph by leveraging [D3](https://d3js.org/)'s `tree` layout.