If you're only interested in viewing a markdown formatted document from a given URL have a look at Markdown Styler.
It supports appending the URL to your markdown document as GET parameter:
https://matteobrusa.github.io/md-styler/?url=https://my.site/my/url.md
Disclaimer: I'm the author of Markdown Styler, which I have created to show formatted markdown documents from Dropbox shared links.
