docs: update README to add link to open A11y Fundamentals section (#331)

Author: wo-o29

README.md

@@ -19,7 +19,7 @@ https://frontend-fundamentals.com/code-quality/en/
 
 - [Code Quality Fundamentals](https://frontend-fundamentals.com/code-quality/)
 - [Bundling Fundamentals](https://frontend-fundamentals.com/bundling/)
-- A11y Fundamentals (coming soon!)
+- [A11y Fundamentals](https://frontend-fundamentals.com/a11y/)
 
 ## Contributing