Convert from GitHub Flavored Markdown to Godot Richtext.
Download the most recent release and extract it into the root of your project.
This creates a res://bin and a res://fonts/libmarkdown directory.
You can then call the conversion method with Markdown.convert_markdown(markdown_formatted_string).
RichTextLabels need a very verbose font setup right now.
I've included some of the Google Noto fonts and the project is preconfigured to use them.
If you want to use different fonts, have a look at the demo project for an example.
You need a DynamicFont for regular, italics, bold, bold italics and monospaced text.
You also need to set the fonts for the six heading fonts in res://fonts/libmarkdown/ because you can't change font size in Godot richtext without creating a new font of that size.