doc: freethreaded support changelog (#2497)

Support is implemented, just documenting this is left.

Fixes #2386

Author: aignas

CHANGELOG.md

@@ -65,6 +65,11 @@ Unreleased changes template.
   automatically includes corresponding stub packages for third-party libraries
   that are present and used (e.g., `boto3` → `boto3-stubs`), improving 
   type-checking support.
+* (pypi) Freethreaded packages are now fully supported in the
+  {obj}`experimental_index_url` usage or the regular `pip.parse` usage.
+  To select the free-threaded interpreter in the repo phase, please use
+  the documented [env](/environment-variables.html) variables.
+  Fixes [#2386](https://github.com/bazelbuild/rules_python/issues/2386).
 
 {#v0-0-0-removed}
 ### Removed