Document auto_now not updating inside of bulk_update_with_history

[twolfson]

Problem Statement
When using bulk_update_with_history, a DateTimeField using auto_now doesn't automatically update like it does with Model.save()

This is technically a deeper Django issue, however this is good to document in a repo which stands on such bulk update conventions as well as well as using Model._default_manager.

Describe the solution you'd like
Update "Common Issues" documentation to spread awareness of issue (took us a year to catch) and how to mitigate it

Describe alternatives you've considered
I already have a working solution, this is strictly documenting/sharing for others

Additional context