Emacs 31 has built-in markdown-ts-mode

[victorolinasc]

Hi and thanks for your work!

Starting from Emacs 31 (which is in pre-RC phase), it will contain a built-in markdown-ts-mode. Rustic depends on markdown implicitly currently. Maybe, to help people not downloading another package from emacs-31 onwards, you could make that dependency conditional and request people to choose which one to use. In the future this dependency can, perhaps, be removed.

Anyway, not a big issue or problem here, just some feature request.

Thanks!

[CeleritasCelery]

If you put together a merge request we can add that feature.