Update Django section (#4759)

* * Updated Django section
- Added link to Django Documentation, version 3.1, in brazilian portuguese

* * Removed version specification in the link and change the suggestion to alphabetical order

free-programming-books-pt_BR.md

@@ -1,4 +1,4 @@
-### Índice
+### Índice
 
 * [Agnósticos](#agnosticos)
   * [Programação](#programação)
@@ -304,6 +304,7 @@
 
 #### Django
 
+* [Documentação do Django](https://docs.djangoproject.com/pt-br)
 * [Tutorial Django Girls](https://tutorial.djangogirls.org/pt/)