This package (at the time this ticket was created) uses relative paths to embed images from their Git repo into their readme:
An example image embed is:
It looks like the markdown renderer we use supports setting a base URL for link resolution.
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.