Docs: Instruction to install django-simple-history before exectuing runtests.py is missing

CHANGES.rst

@@ -15,6 +15,7 @@ Unreleased
 - Added temporary requirement on ``asgiref>=3.6`` while the minimum required Django
   version is lower than 4.2 (gh-1261)
 - Small performance optimization of the ``clean-duplicate_history`` command (gh-1015)
+- Added ``pip install django-simple-history`` command in the Testing section of CONTRIBUTING.rst (gh-1293)
 - Support Simplified Chinese translation (gh-1281)
 
 3.4.0 (2023-08-18)

CONTRIBUTING.rst

@@ -65,7 +65,7 @@ To run tox and generate an HTML code coverage report (available in the
     make test
 
 To quickly run the tests against a single version of Python and Django (note: you must
-``pip install django`` beforehand)::
+``pip install django`` and ``pip install django-simple-history`` beforehand)::
 
     python runtests.py