5800 atest readme - #5802

I looked at this quickly, and noticed that you created the table of contents as a list. Apparently GFM doesn't support automatic TOC generation similarly as reST. Having a TOC would be nice, but manually maintaining it isn't worth the effort.

Another observation is that directory contents don't render that well. It was a definition list in reST, but Markdown doesn't support them. It could be turned to a two-column table or to normal list similarly as tags are shown in another section.

It's annoying that GFM doesn't make headings reference targets. It would be convenient that if you have, for example, # Example, you could refer to it like [example] instead of needing to use [example](#example).

If a link is needed multiple times, or the target is long, creating an explicit reference target like in this example is often a good idea, though:

The [run.py] script does something.

[run.py]: run.py

Should we have some kind of a recommendation when to create reference targets and where to add them?

Converted PR to draft, so that I can address the review comments