Add content author's link

[lukaszstolarczuk]

Add links to GitHub for authors of the content. Right now we only state the author by their name. We could also add a link to GH profiles, based on a login delivered as a separate metadata, e.g., in blog content.

# Blog post creation date
date: 2022-01-26

# Blog post author and GH link
author: "Łukasz Stolarczuk"
gh-link: lukaszstolarczuk

I believe this would be a nice addition and could make a way for readers to contact us easier.

It applies to all archetypes, which inform about the content's user.