And one often touted by @BLUEFROG before.
You might want to take a look at Script: Convert Markdown to TextBundle with images included. The script builds a TextBundle from an MD file, grabbing all images referenced in the MD. Instead of doing this, it could be modified to create a group and a subgroup assets, moving the MD file to the former and the images to the latter (or copying if moving is too intrusive). The changes should be minimal.