We are in the final stages of creating this part of the documentation, after which it will be displayed on this page.
In the meanwhile you can generate it yourself from the Unbound source:
After ./configure --with-pyunbound run make doc which builds the documentation in doc/html/pyunbound.
It is also possible to run sphinx-build -b html libunbound/python/doc doc/html/pyunbound/ without compiling.
The html will end up in the doc/html/pyunbound directory, open index.html with the web browser to see the content.
