Please add Django 2.0 Online Book (#2691)

* Please add Django 2.0 Online Book

I would like to add this online book of Django 2.0 to the list.

Thanks in advance.

* Django 2.0 Tutorial for Beginners

Removed slash "/" at the end of link.
(Although several other links contain it)

free-programming-books.md

@@ -1959,6 +1959,7 @@ For resources on Angular, Backbone, D3, Dojo, Ember, Express, jQuery, Knockout,
 
 #### Django
 
+* [Django 2.0 Tutorial for Beginners](https://djangoforbeginners.com) (2.0)
 * [Django Girls Tutorial](https://tutorial.djangogirls.org/en/) (1.11)
 * [Django Official Documentation](https://media.readthedocs.org/pdf/django/1.5.x/django.pdf) (PDF) (1.5)
 * [Django Official Documentation](https://media.readthedocs.org/pdf/django/1.7.x/django.pdf) (PDF) (1.7)