Update free-courses-en.md (#10875)

* Update free-courses-en.md

## What does this PR do?
Add web accessibility resource(s)

## For resources
### Description
Web Accessibility – What It Is and How to Design for It

### Why is this valuable (or not)?
Yes, this is valuable.

### How do we know it's really free?
It is available on YouTube.

### For book lists, is it a book? For course lists, is it a course? etc.
It is a tutorial.

## Checklist:
- [ ] Read our [contributing guidelines](https://github.com/EbookFoundation/free-programming-books/blob/main/docs/CONTRIBUTING.md).
- [ ] [Search](https://ebookfoundation.github.io/free-programming-books-search/) for duplicates.
- [ ] Include author(s) and platform where appropriate.
- [ ] Put lists in alphabetical order, correct spacing.
- [ ] Add needed indications (PDF, access notes, under construction).
- [ ] Used an informative name for this pull request.

## Follow-up

- Check the status of GitHub Actions and resolve any reported warnings!

* Update free-courses-en.md

courses/free-courses-en.md

@@ -1667,6 +1667,7 @@
 * [React Fundamentals - The Complete Guide For Beginners](https://www.udemy.com/course/react-fundamentals-the-complete-guide-for-beginners/) - Kerim Abdelmouiz (Udemy)
 * [The GraphQL Apollo (with ReactJS, NodeJS and MongoDB)](https://www.udemy.com/course/the-new-graphql-apollo-course-2020) - Mohd. Raqif Warsi (Udemy)
 * [The Odin Project - Learn Web Development for Free](http://www.theodinproject.com)
+* [Web Accessibility – What It Is and How to Design for It?](https://www.hostinger.in/tutorials/web-accessibility) - Hostinger Tutorials
 * [Web Basics](https://open.cs.uwaterloo.ca/web-basics/) - Centre for Education in Math and Computing (University of Waterloo)
 * [Web Development Course](https://syllabus.migracode.org/courses/introduction-3) - MigraCode Barcelona
 * [Web Development for Beginners - A Curriculum](https://github.com/microsoft/Web-Dev-For-Beginners) - Microsoft