Suggestion: Update this repo's "About" blurb to mention it's a fork for adding free-threaded python support

[jimkring]

Scenario (issue)

As a python user who happens upon this repository (e.g. when looking at someone's github actions yaml or some other entry point to this repo's home page), it would be helpful to know why this repo exists and what's different about it than the canonical actions/setup-python action.

Possible Solution

• Update this repo's "About" blurb to mention it's a fork for adding free-threaded python support

For example, here:

Alternative Ideas:

• Update the README.md with a note about it
• Rename the repo/url to Quansight-Labs/setup-python-with-freethreaded