doc: pytest: Framework for documenting tests and document test_000_version

doc: pytest: Framework for documenting tests and document test_000_version

In order to easily document pytests, we need to include the autodoc
extension. We also need to make sure that for building the docs, CI
includes pytest and that we have PYTHONPATH configured such that it will
find all of the tests and related files. Finally, we need to have our
comments in the test file by in proper pydoc format in order to be
included in the output.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>