This library is still very experimental; proceed at your own risk.
The directory PureDataP5 contains the source code and dependencies, configured for development on Mac OS. You won't need to look at this unless you want to participate in the development of this library.
If you just want to use libpd with Processing, then you can unpack the file pdp5.zip into the libraries folder of Processing. On my Mac, that folder is Documents/Processing/libraries.