feat: add new resource for next.js (#7631)

* feat: add new resource for next.js

* fix: update title and author

* fix: alphabetical order

* fix: line spacing

books/free-programming-books-langs.md

@@ -1242,6 +1242,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 
 #### Next.js
 
+* [Learn Next.js](https://nextjs.org/learn) - Vercel Inc.
 * [Mastering Next.js](https://masteringnextjs.com)
 * [Next.js Crash Course 2021](https://www.youtube.com/watch?v=mTz0GXj8NN0) - Brad Traversy (Traversy Media)
 * [The Next.js Handbook](https://flaviocopes.com/page/nextjs-handbook/) - Flavio Copes (PDF, EPUB, Kindle) *(email address requested)*