Context

Let's call this out more prominently under an "Unavoidable breaking changes" section like we do here: https://github.com/mongodb/mongo-python-driver/blob/3d63eedb/doc/changelog.rst?plain=1#L291

It's also best practice to show how this breaking change could show up and what to do about it. Including example code that expects CommandStartedEvent.command to be SON would be good.

Definition of done

Above mentioned changes

Pitfalls

None