Declare support for Django 4.0

Author: Photonios

README.md

@@ -8,7 +8,7 @@
 | :memo: | **License** | [![License](https://img.shields.io/:license-mit-blue.svg)](http://doge.mit-license.org) |
 | :package: | **PyPi** | [![PyPi](https://badge.fury.io/py/django-postgres-extra.svg)](https://pypi.python.org/pypi/django-postgres-extra) |
 | :four_leaf_clover: | **Code coverage** | [![Coverage Status](https://coveralls.io/repos/github/SectorLabs/django-postgres-extra/badge.svg?branch=coveralls)](https://coveralls.io/github/SectorLabs/django-postgres-extra?branch=master) |
-| <img src="https://cdn.iconscout.com/icon/free/png-256/django-1-282754.png" width="22px" height="22px" align="center" /> | **Django Versions** | 2.0, 2.1, 2.2, 3.0, 3.1, 3.2 |
+| <img src="https://cdn.iconscout.com/icon/free/png-256/django-1-282754.png" width="22px" height="22px" align="center" /> | **Django Versions** | 2.0, 2.1, 2.2, 3.0, 3.1, 3.2, 4.0 |
 | <img src="http://www.iconarchive.com/download/i73027/cornmanthe3rd/plex/Other-python.ico" width="22px" height="22px" align="center" /> | **Python Versions** | 3.6, 3.7, 3.8, 3.9, 3.10 |
 | :book: | **Documentation** | [Read The Docs](https://django-postgres-extra.readthedocs.io/en/master/) |
 | :warning: | **Upgrade** | [Upgrade from v1.x](https://django-postgres-extra.readthedocs.io/en/master/major_releases.html#new-features)
@@ -59,7 +59,7 @@ With seamless we mean that any features we add will work truly seamlessly. You s
 ### Prerequisites
 
 * PostgreSQL 10 or newer.
-* Django 2.0 or newer (including 3.x).
+* Django 2.0 or newer (including 3.x, 4.x).
 * Python 3.6 or newer.
 
 ### Getting started