Support relative image paths in readmes from GitHub

This package (at the time this ticket was created) uses relative paths to embed images from their Git repo into their readme:

https://www.forgebox.io/view/commandbox-cflint

An example image embed is:

Which Github resolves to
https://raw.githubusercontent.com/jsteinshouer/commandbox-cflint/master/examples/cflint-console-example.png

It looks like the markdown renderer we use supports setting a base URL for link resolution.
https://github.com/vsch/flexmark-java/wiki/Customizing-Docx-Rendering#image-embedding

We just need to check and see if their box.json has a GitHub repo set up and auto-create the base URL for their links. We can also see if BitBucket allows for this and what their base URL looks like.