at the moment to have image renders reliably with .adoc you need to do something like:

ifdef::env-github[]
:imagesdir: https://github.com/maxandersen/jbang/blob/master
endif::[]

this works great but when you are doing Pull requests and forks your images wont work unless they exist in that master branch.

Suggestion is that there would be a github-location attribute with the https path for the base of the repo, like: https://github.com/maxandersen/jbang/blob/master or if in a branch https://github.com/maxandersen/jbang/blob/custombranch or in a fork https://github.com/ditto/jbang/blob/master

with that rendering would "just work".