I'm also experiencing this, unfortunately. GitHub and other similar hosting services appear to support this case fine, though.

Hmm, okay. Could there perhaps be some way to use builds.sr.ht to set what git.sr.ht's project page shows, then?

It would be nice to see AsciiDoc be supported by the README renderer on project homepages.

There's two implementations that would do a good job to fill this role...

• asciidoc3 is recently finished port of the original Python 2 asciidoc interpreter to Python 3. It has a Python API that could be used directly.
• asciidoctor, which is used by GitHub, but unfortunately lacks a Python module of any sort, being written in Ruby. Just calling the interpreter is an option but that's not very ideal. It has a few extensions over the original though. In my opinion it's got more people using it, though.