We already have a ["HOWTO" guide](https://docs.python.org/3.13/howto/free-threading-extensions.html#freethreading-extensions-howto) for free-threading C API extension authors. We should have a similar guide aimed at people writing Python code. The HOWTO should document the current limitations of the free-threaded build. <!-- gh-linked-prs --> ### Linked PRs * gh-124371 * gh-124860 <!-- /gh-linked-prs -->