Added How to Meet WCAG (Quick Reference) (#7741)

* Added How to Meet WCAG (Quick Reference)

A customizable quick reference to Web Content Accessibility Guidelines (WCAG) 2 requirements (success criteria) and techniques. From W3C WAI

* Used the title given by the resource*, No editorial descriptions.

*I still think that it's needed to refer to WCAG with their full name, so that folks that don't know them by acronym see the Accessibility part. Hope that's OK (title in code is actually `<h1>How to Meet <abbr title="Web Content Accessibility Guidelines">WCAG</abbr>  (Quick Reference)</h1>`)

courses/free-courses-en.md

@@ -1154,6 +1154,7 @@
 * [Frontend UI Development with React](https://www.youtube.com/playlist?list=PL0vfts4VzfNgUUEtEjxDVfh4iocVR3qIb) - Jeff Delaney, Fireship.io (YouTube)
 * [Full Stack Foundations](https://www.udacity.com/course/full-stack-foundations--ud088) - by AWS on Udacity
 * [Full stack open](https://fullstackopen.com/en/) - University of Helsinki, Houston Inc., Terveystalo, Elisa, K-ryhmä, Unity Technologies, Konecranes
+* [How to Meet Web Content Accessibility Guidelines (Quick Reference)](https://www.w3.org/WAI/WCAG21/quickref/) - W3C Web Accessibility Initiative
 * [Introduction to Professional Web Development in JavaScript](https://education.launchcode.org/intro-to-professional-web-dev/) - Chris Bay, Jim Flores, Blake Mills, Sally Steuterman, Paul Matthews, Carly Langlois (The LaunchCode Foundation)
 * [Java Web Development](https://education.launchcode.org/java-web-development/) - Chris Bay, Jim Flores, Carly Langlois, Sally Steuterman (The LaunchCode Foundation)
 * [Learn web development](https://developer.mozilla.org/en-US/docs/Learn) - Mozilla Contributors