It would be a very nice feature if not only the README is rendered with Markdown or the like, but instead //every// file, that contains Markdown-Code. Or, more easier to implement, every *.markdown file. For example: README.markdown, CHAGELOG.markdown, TODO.markdown.
It should be rendered if one clicks on the file in the source-tab. So to speak don't show the RAW file by default, but the Markdown rendered file.