Added New Django Rest Framework PDF (#7220)

* Added Django Rest Framework Free PDF

* Added New Django Rest Framework PDF

* Add RIPTutorial author notes

* Alphabetize

Co-authored-by: David Ordás <3125580+davorpa@users.noreply.github.com>

books/free-programming-books-langs.md

@@ -1947,6 +1947,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Django Official Documentation](https://buildmedia.readthedocs.org/media/pdf/django/2.2.x/django.pdf) (PDF) (2.2)
 * [Django Official Documentation](https://buildmedia.readthedocs.org/media/pdf/django/3.1.x/django.pdf) (PDF) (3.1)
 * [Django Official Documentation](https://buildmedia.readthedocs.org/media/pdf/django/3.2.x/django.pdf) (PDF) (3.2)
+* [Django Rest Framework](https://riptutorial.com/Download/django-rest-framework.pdf) - Compiled from StackOverflow Documentation (PDF)
 * [Django RESTful Web Services](https://www.packtpub.com/free-ebooks/django-restful-web-services) - Gaston C. Hillar (Packt account *required*)
 * [Django Web Framework (Python)](https://developer.mozilla.org/en-US/docs/Learn/Server-side/Django) - MDN contributors
 * [Djen of Django](http://agiliq.com/books/djenofdjango/)