add Quarto to documentation

[VladimirAlexiev]

Describe your proposed improvement and the problem it solves.
I want to add https://quarto.org/
to https://pandoc.org/extras.html#academic-publishing-workflows

Where is extras.md?

[tarleb]

It's in a different repo here: https://github.com/jgm/pandoc-website/blob/master/extras.md

[jgm]

I'm going to move extras.md over to this repo so it's with the other docs.
(Done)