Support for footnotes

[lylo]

I've had a surprising number of requests for footnote support in Pagecord so I thought I'd start a discussion here on the possibility. ProseMirror has an implementation which could serve as inspiration: https://prosemirror.net/examples/footnote/

TipTap has a plug-in too: https://github.com/buttondown/tiptap-footnotes.

Would anyone else find this feature useful?