Since v.0.16.0 MS Powertoys can perform the same task. Given that my setup is buggy and poorly supported, I recommend using MS Powertoys.
It was fun to develop this tool, less fun debugging it.
Thanks @Aaltuj for the heads up
A Windows Explorer preview pane handler for Markdown files
Inspired by SharpShell, a well documented framework for creating Windows Shell Extensions, combined with my search for a preview handler for .md files this tiny project was born.
It displays .md files as MarkDown in the Windows Explorer preview pane
Download and run the latest installer from MarkdownPreview releases on GitHub.
Next to SharpShell, this project uses MarkDig styled by MarkdownPad CSS.
Sample preview (taken in Windows Explorer in Windows 10)