Link to django_stubs_ext is broken

[Flimm]

In the README.md file, there is this section:

You can get a TypeError: 'type' object is not subscriptable when you will try to use QuerySet[MyModel], Manager[MyModel] or some other Django-based Generic types.

This happens because these Django classes do not support __class_getitem__ magic method in runtime.

1. You can go with django_stubs_ext helper, that patches all the types we use as Generic in django.

   Install it:

   pip install django-stubs-ext  # as a production dependency

   And then place in your top-level settings:

   import django_stubs_ext
   
   django_stubs_ext.monkeypatch()

   You can add extra types to patch with django_stubs_ext.monkeypatch(extra_classes=[YourDesiredType])

2. You can use strings instead: 'QuerySet[MyModel]' and 'Manager[MyModel]', this way it will work as a type for type-checking and as a regular str in runtime.

As a newcomer to types in Python, I find this whole section confusing. But the bug I want to report is that the link to django_stubs_ext is broken. The directory django_stubs_ext doesn't seem to exist any more.