Added a badge with BrowserStack status. [skip ci]

Author: Kamil Piechaczek

README.md

@@ -4,6 +4,7 @@ CKEditor 5 utilities
 [![Join the chat at https://gitter.im/ckeditor/ckeditor5](https://badges.gitter.im/ckeditor/ckeditor5.svg)](https://gitter.im/ckeditor/ckeditor5?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 [![npm version](https://badge.fury.io/js/%40ckeditor%2Fckeditor5-utils.svg)](https://www.npmjs.com/package/@ckeditor/ckeditor5-utils)
 [![Build Status](https://travis-ci.org/ckeditor/ckeditor5-utils.svg?branch=master)](https://travis-ci.org/ckeditor/ckeditor5-utils)
+[![BrowserStack Status](https://www.browserstack.com/automate/badge.svg?badge_key=d3hvenZqQVZERFQ5d09FWXdyT0ozVXhLaVltRFRjTTUyZGpvQWNmWVhUUT0tLUZqNlJ1YWRUd0RvdEVOaEptM1B2Q0E9PQ==--c9d3dee40b9b4471ff3fb516d9ecf8d09292c7e0)](https://www.browserstack.com/automate/public-build/d3hvenZqQVZERFQ5d09FWXdyT0ozVXhLaVltRFRjTTUyZGpvQWNmWVhUUT0tLUZqNlJ1YWRUd0RvdEVOaEptM1B2Q0E9PQ==--c9d3dee40b9b4471ff3fb516d9ecf8d09292c7e0)
 [![Test Coverage](https://codeclimate.com/github/ckeditor/ckeditor5-utils/badges/coverage.svg)](https://codeclimate.com/github/ckeditor/ckeditor5-utils/coverage)
 [![Dependency Status](https://david-dm.org/ckeditor/ckeditor5-utils/status.svg)](https://david-dm.org/ckeditor/ckeditor5-utils)
 [![devDependency Status](https://david-dm.org/ckeditor/ckeditor5-utils/dev-status.svg)](https://david-dm.org/ckeditor/ckeditor5-utils?type=dev)