To install, do this:
mkdir -p build
cd build
cmake ..
make parser
make install

IMPORTANT: If you're using Arch Linux: Arch breaks the standard of having "python" point to a python2 implementation. This breaks stuff.
So if you're using arch, either make "python" call some python2 interpreter instead of python3 while compiling (only while compiling, doesn't matter afterwards)
or edit the file python-src/Parser/asdl_c.py and change the first line to point to your python2 implementation, so usually replace
#! /usr/bin/env python
with
#! /usr/bin/env python2

Another notice for arch users: The plugin queries your default python interpreter for module search paths. So, if you want to use django for example and it's installed
in some python2 module directory, and python3 is your default interpreter, you won't get autocompletion (or anything) for it. You can easily solve that by adding
the directory in question to the $PYTHONPATH environment variable (':' is the seperator, if you want more than one path) and restarting kdevelop.