Document transition to core bundle classes or continuing use case

Problem/Motivation

Core got bundle classes in version 9.3: https://www.drupal.org/node/3191609 →

Proposed resolution

Document transitioning to the core functionality and mark this module deprecated ("moved into core woohoo!") or document what makes using this module a good idea still.

Or at least mention core bundle classes as an option (this module's page has better SEO than core's documentation, heh).