Render markdown images present in github repos or OSF storage

[mdingemanse]

Markdown rendering is fairly rudimentary and currently excludes images. I was hoping to see functionality like github's, where markdown files are rendered in full if they include relative references to images present in the repository. Presumably github does some work to make relative links like [](out/map-1.png) show up in the in-browser rendering of the .md? It even works in their readme.md, which makes for nice repo landing pages.

For security reasons, it would make sense of course to limit rendered image links to images available in the project storage or in the linked storage (e.g. github repo).

Having this functionality would make OSF perfect for sharing view-only links to reproducible work. These view-only links are indispensable for blind submissions, which are still common in many disciplines. Currently, such view-only links force reviewers to download .md or .html files before they can see the material.