This package appears to contain a pickled cache of reStructuredText (*.rst) documentation in a .doctree file.
These are not needed to display the documentation correctly and as they can contain absolute build paths can affect the reproducibility of the package.
Either prevent the installation of the .doctree file (or parent doctrees directory if there is one) or pass the -d option to sphinx-build(1) to create the caches elsewhere.
override_dh_auto_build: dh_auto_build PYTHONPATH=. sphinx-build -bman docs/ -d debian/doctrees docs/build/html PYTHONPATH=. sphinx-build -bhtml docs/ -d debian/doctrees docs/build/html
override_dh_auto_clean: dh_auto_clean rm -rf debian/doctrees
Refer to http://sphinx-doc.org/invocation.html#cmdoption-sphinx-build-d for details.