Support rendering markdown files besides README.md

[KyleJune]

It's common for README.md files to link to other markdown files. On GitHub, when you click one of those links it will take you to a page with the markdown rendered instead of the source code for the markdown file. On JSR, those links take you to the source code for the markdown files.

You can see an example of this by clicking any of the links near the bottom of the overview for my package.

https://jsr.io/@udibo/react-app

[inverted-capital]

This problem is compounded further if the package is published out of a monorepo / workspace. What happens is the linked repository is the workspace root, and the links to the markdown docs are generated relative to that, not relative to the package subdirectory in that root.

The package markdown should render relative links that stay on the jsr site, and show the file in the files view, imo