This also the problem with README.md. Markdown is a format for writing html codes in a typewriter plain text style, adored within the culture of programmers. Popular code hosting site Github renders README.md for you. But when you download a software package including such a file, it breaks in much the same way as an extensionless README does: A novice user does not know with which program to open it, and the Operating System is not able to give a preview.
Thanks for the pull request, Jon.
However, I’d prefer not to. Quoting from a blog post on the subject of extensions of README files: