Change origin of md relative links

[alexdln]

Some projects (like here) have relative links to other readme files and other internal md files within the readme.

For everything except md, everything looks correct, but for md - the links start pointing to jsdelivr with a 404 error.

We need to specify the user's Github origin for such links (just like npm)

Links to https://cdn.jsdelivr.net/npm/robindoc/docs/03-customization/README.md

Warning

If GitHub is unknown, we should leave the links unchanged (npm has the same behavior) (example pkg)