GraphComment is an alternative to Disqus, which in my opinion looks a bit cluttered. GraphComment has a more clean look to me.
You need to sign up on https://www.graphcomment.com and get a free ID.
Usage:
Copy graphcomment.html to /layout/shortcodes/graphcomment.html
On your *.md page add {{< graphcomment >}} where the comments should show.
In your config.toml add your graphcomment ID:
[params]
graphcommentId = "YOUR-ID-HERE"
You can also import comments from Wordpress (only with the Wordpress app though), moderate comments on the graphcomment.com website. Their SPAM protection also works nicely.