And read-me files are for, <gasp>, READING. Not writing. I have no need to EDIT any Markdown files... pretty much ever. Nor do I need to clutter my IDE with tabs devoted to reference material, much less an extra pane to "preview" it in its intended rendering.

Your pretension that most programming involves writing Markdown "source code" is absurd. I neither want nor need Markdown in any of my source-code editors, ever. Not once in decades of professional programming have I missed it.

And if I do need to create Markdown, I will want to do so in a simple WYSIWIG editor and save it as MD. Again... not in my IDE.