Add list with more resource on free-threading & CPython internals

[lysnikolaou]

Certainly not an exhaustive list. Open to more suggestions on what to include here!

[rgommers]

Thanks @lysnikolaou for putting this together! As for what else to add, a few things come to mind:

• https://facebookincubator.github.io/ft_utils/
• the key Discourse threads with the discussions about PEP 703 and the announcement from the Steering Council to accept it
• perhaps some blog posts, e.g., https://labs.quansight.org/blog/free-threaded-python-rollout and https://til.simonwillison.net/python/trying-free-threaded-python
• perhaps other talks, e.g. Keynote: The big leap of Python 3.13 - Łukasz Langa, Anthony Shaw: Unlocking the Parallel Universe: Subinterpreters and Free-Threading in Python 3.13.

[lysnikolaou]

Thanks for the recommendations @rgommers! Added all of them to the list.

[rgommers]

This looks good, in it goes! We can always add more resources later.