Adopt Sphinx Playground to create reproducers

[flying-sheep]

Hi @AA-Turner! I made a little gift for Sphinx: https://flying-sheep.github.io/doc-play/

It’s intended to

1. become part of the issue template so people can use it to create reproducers
2. Go into this org! If you’re interested, I can give you ownership access so you can transfer it. I think it should become https://github.com/sphinx-doc/play, so it can be https://play.sphinx-doc.github.io, but of course becoming https://play.sphinx-doc.org would be even better.

I tried to reach you on Discord, but you didn’t reply, so I’m trying this route.