TIL: Setting Kramdown Options for Jekyll
Kramdown is the default (and preferred) markdown processor for Jekyll.
Despite a laundry list of support options listed on the Jekyll site, there was not any details on how to set one of the configuration overrides. After a few guesses, I got it set up properly. Just add the following (and another other options you want) to your _config.yml file:
markdown: kramdown kramdown: footnote_backlink: '↩︎'