Add comments system

[stefanv]

Adding comments will allow us to publish slightly more controversial opinion pieces, since the community will then be able to add different perspectives.

Consider public hosted tools such as (update list as you find options):

• https://github.com/giscus/giscus
• https://github.com/utterance/utterances (not sure it's being maintained?

See also https://gohugo.io/content-management/comments/

[stefanv]

Discourse is another option, but it requires people having an account. GitHub accounts are more likely to pre-exist.