[3.14] gh-119180: More documentation for PEP 649/749 (GH-133552) (#133902)

gh-119180: More documentation for PEP 649/749 (GH-133552)

The SC asked that the Appendix in PEP-749 be added to the docs.
(cherry picked from commit 3396df56d0849e5154cb7d7d1c525df834bbe15e)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>