request: support markdown footnotes in READMEs

[olets]

A widespread Markdown extension is footnotes. See https://www.markdownguide.org/extended-syntax/#footnotes. It'd be great if READMEs supported a footnote extension.

Compare e.g. https://jsr.io/@olets/css-fluid-length, where footnote-y syntax becomes in-place links, and https://codeberg.org/olets/css-fluid-length, where the same renders with footnotes.