I basically followed the very clear instructions set up on this blog post. There are instructions there for setting up a GitHub hosting account (which is free, for some reason, if you’re using Jekyll), setting up a domain name to point to the GitHub host, setting up Google Analytics, and setting up the Disqus commenting system.
Make a Disqus account.
Create a short-name by registering here.
Enable Disqus by setting the disqus-shortname variable in the Jekyll config file.
Set “comments: true” in the YAML front matter of any post that you want commenting enabled on!