docs: document how to run the tests on MySQL locally

mysql_test_settings.py

@@ -7,6 +7,14 @@
 The tox targets for py38-django32 and py38-django42 will use this settings file.
 For the most part, you can use test_settings.py instead (that's the default if
 you just run "pytest" with no arguments).
+
+If you need a compatible MySQL server running locally, spin one up with:
+docker run --rm \
+    -e MYSQL_DATABASE=test_oel_db \
+    -e MYSQL_USER=test_oel_user \
+    -e MYSQL_PASSWORD=test_oel_pass \
+    -e MYSQL_RANDOM_ROOT_PASSWORD=true \
+    -p 3306:3306 mysql:8
 """
 
 from test_settings import *