[py] Fix theme name

Author: cgoldberg

py/docs/README.rst

@@ -39,8 +39,8 @@ dependencies. Then tox runs the ``sphinx-autogen`` command to generate autodoc s
 Then it runs ``sphinx-build`` to build the HTML docs.
 
 Sphinx is .. well a much larger topic then what we could cover here. Most important to say
-here is that the docs are using the "sphinx_rtd_theme" theme (AKA "Read the Docs" theme) and
-the the majority of the api documentation is autogenerated. There is plenty of information
+here is that the docs are using the "sphinx-material" theme (AKA "Material for Sphinx" theme)
+and the the majority of the api documentation is autogenerated. There is plenty of information
 available and currently the documentation is fairly small and not complex. So some basic
 understanding of reStructuredText and the Sphinx tool chain should be sufficient to contribute
 and develop the Python docs.