Documentation

[tarleb]

The README should be updated with the following information:

• description of the images do we provide; (add CircleCI build and docs #12)
• using images to convert documents (document usage *and* github actions #23)
• building custom images from existing ones (Documentation #9)
• links to other resources (pandoc manual, docker howto?) (document usage *and* github actions #23, link to pandoc / manual, current latest=2.7 #31)
• license (add CircleCI build and docs #12)

[maxheld83]

as suggested by @svenevs I actually documented usage and pointed to github actions, while I was at it 😄 . Makes a lot of sense, because users really need to understand the former to use the latter.

[svenevs]

links to other resources (pandoc manual, docker howto?);

what else do we want in this section? TBH there's no single source of truth for docker...

[tarleb]

The docker links in the README are quite good already. We should mention https://pandoc.org/MANUAL.html somewhere in there.