Readme: add codesponsor.io badge

Author: rstacruz

Readme.md

@@ -9,6 +9,8 @@ Medium.
 [![Status](https://api.travis-ci.org/rstacruz/nprogress.svg?branch=master)](http://travis-ci.org/rstacruz/nprogress) 
 [![npm version](https://img.shields.io/npm/v/nprogress.png)](https://npmjs.org/package/nprogress "View this project on npm")
 
+<a target='_blank' rel='nofollow' href='https://app.codesponsor.io/link/mpgUepSsuAMdpQbEST7TWH6T/rstacruz/nprogress'>  <img alt='Sponsor' width='888' height='68' src='https://app.codesponsor.io/embed/mpgUepSsuAMdpQbEST7TWH6T/rstacruz/nprogress.svg' /></a>
+
 Installation
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