add saucelabs badge

Author: maraoz

README.md

@@ -4,6 +4,7 @@ Bitcore
 [![NPM Package](https://img.shields.io/npm/v/bitcore.svg?style=flat-square)](https://www.npmjs.org/package/bitcore)
 [![Build Status](https://img.shields.io/travis/bitpay/bitcore.svg?branch=master&style=flat-square)](https://travis-ci.org/bitpay/bitcore)
 [![Coverage Status](https://img.shields.io/coveralls/bitpay/bitcore.svg?style=flat-square)](https://coveralls.io/r/bitpay/bitcore)
+[![Sauce Test Status](https://saucelabs.com/browser-matrix/maraoz.svg)](https://saucelabs.com/u/maraoz)
 
 A pure and powerful JavaScript Bitcoin library.