Add support for comments

[hellais]

For a brief window of time (couple of hours), I enabled comments via disqus, thinking it would fit our use case.

However their claim to support "anonymous" comments is a lie (they actually require an email address to post "guest" comments), the UI is very intrusive (it contains a bunch of spam from disqus) and in general it's probably not nice to send data to some third party whenever they read our articles.

To this end I think we should look into adding support for comments via some hosted alternative. I found this thing: https://github.com/posativ/isso/, that seems to be fairly well maintained and support the features we need (truly anonymous comments, minimal UI and self-hosted).

I would say we set this up and try it out on our post pages.