Github pages are static html files generated from text-only markdown files hosted on github.com. Since they are static, there is no way to dynamically generate content, and you can’t use a normal comment system.
But we do have a solution.
It’s disqus.
What you need to do is:
- Create an account in disqus
 - Register your site for free
 - 
    
Copy-paste two blocks of auto generated javascipt codes to
yourname.github.io\_layouts\post.html 
This step might be diffcult for js-noobs like me, refer to my implemetation if you feel dizzy.
The two blocks starts with
<!-- disqus loading -->  and 
<!-- disqus rendering -->