[markdown] How to add footnotes to GitHub-flavoured Markdown?

Expanding on the previous answers even further, you can add an id attribute to your footnote's link:

 Bla bla <sup id="a1">[1](#f1)</sup>

Then from within the footnote, link back to it.

<b id="f1">1</b> Footnote content here. [?](#a1)

This will add a little ? at the end of your footnote's content, which takes your readers back to the line containing the footnote's link.