small fix to the description (#70)

Fixed where it mentioned "Django Rest Framework", the old wording leads us to believe it had to do with DRF instead of Django Ninja

Author: CarlosBueno99

docs/index.md

@@ -11,7 +11,7 @@ A JSON Web Token authentication plugin for the [Django Ninja REST Framework](htt
 ------------------------------------------------------------------------
 
 Ninja JWT provides a JSON Web Token authentication backend for the
-Django REST Framework. It aims to cover the most common use cases of
+Django Ninja REST Framework. It aims to cover the most common use cases of
 JWTs by offering a conservative set of default features. It also aims to
 be easily extensible in case a desired feature is not present.