Take a look at the "ReST Builder" extension: https://pythonhosted.org/sphinxcontrib-restbuilder/.
There's not much to say; the extension takes reST as input and outputs ...drumroll... reST!
Quote:
This extension is in particular useful to use in combination with the autodoc extension. In this combination, autodoc generates the documentation based on docstrings, and restbuilder outputs the result are reStructuredText (.rst) files. The resulting files can be fed to any reST parser, for example, they can be automatically uploaded to the GitHub wiki of a project.