The :include: restructuredtext directive (http://docutils.sourceforge.net/docs/ref/rst/directives.html#including-an-external-document-fragment) looks like it's disabled at the moment. https://github.com/github/markup/blob/master/lib/github/commands/rest2html#L24

Could you enable it, so that I could, for example, put

.. include:: requirements.txt
   :literal:

And it would put the contents of the requirements.txt file into the rendered readme page.