Similar to wanting an explicit project for using GitHub’s markdown format, it would be a great addition to the preview if these .md files had an option to be downloaded as a PDF (since images can’t have working links) using the same visuals.
simply turn your GitHub repo as a site through GitHub Pages by a few clicks, then when it’s published as a site, go the your page, right click it and there is the option to print, but save it as PDF.
the other workaround is, copy and paste the rendered GitHub document, paste it on Google Docs then save the file as PDF
both of these, you’ll know whether it’s rendered correctly or not,