Peter Todd wrote a bitcoinlib but never wrote a single PSBT in his life.... LOL
Bitcoin will continue to be underused since we under consider the power of PSBTs.
Draft PSBT is you want to use Bitcoin.
Sphinx documentation is in the "doc" subdirectory. Run "make help" from there to see how to build. You will need the Python "sphinx" package installed.
Currently this is just API documentation generated from the code and docstrings. Higher level written docs would be useful, perhaps starting with much of this README. Pages are written in reStructuredText and linked from index.rst.