And because of the lack of such readers, everyone just reads the plain text with a bunch of garbage in it. It's just gallingly dumb.
That's what documentation generators are for, to render all the docs and search them if you're just a user.
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.
And how often are you even reading READMEs? For me it's usually once, when I first use a library, because it typically gives an outline of the project and/or instructions on how to install it. So I'm reading it in a browser.
Meanwhile I'm updating my own READMEs often, usually using them as a sort of to-do list and then outlining existing functionality.
Like, are you really using so many libraries as glue that reading READMEs is such a common task that you specifically want it in your IDE? Is that the current state of programming?
Are you being intentionally obtuse? I said that's exactly what I DON'T want.
.gitignore or .ignore file...