• I have searched the issues of this repo and believe that this is not a duplicate.

Issue

When Markdown support was initially added in #15, Warehouse had somewhat questionable Markdown rendering. At this point, however, it appears that those issues have been resolved, and things like syntax highlighting now work.

As such, given the relative popularity of Markdown even for Python projects, it might make more sense for new to default to creating a README.md rather than a README.rst.