Request: Add a step-by-step guide explaining how to get a portable python build on linux

Hello,

Thank your your work on this tool !

I'm trying to get a portable build of python 3.10 out of portable-python and I'm probably missing something because builds are... not portable :'(

Here is what I have tried to far in docker running ubuntu:18.04

apt update && apt install python3-pip gcc make libffi-dev zlib1g-dev
pip3 install portable-python
portable-python build 3.10.9

The build succeeds but the resulting python build is linked against libffi and libz:

        prefix  /build/ppp-marker/3.9.16
          _bz2  *absent* None
       _ctypes  1.1.0 _ctypes*.so ffi:6
       _curses  *absent* None
          _dbm  *absent* None
      _decimal  1.70 _decimal*.so
         _gdbm  *absent* None
         _lzma  _lzma*.so
      _sqlite3  *absent* None
          _ssl  *absent* None
      _tkinter  *absent* None
         _uuid  *absent* None
           pip  22.0.4 lib/python3.9/site-packages/pip
       pyexpat  2.5.0 pyexpat*.so
      readline  *absent* None
    setuptools  58.1.0 lib/python3.9/site-packages/setuptools
          zlib  1.2.11 zlib*.so z:1
  libpython*.a  67 MB lib/libpython3.9.a lib/python3.9/config-3.9-x86_64-linux-gnu/libpython3.9.a
 libpython*.so  -not used-
  install size  122 MB
ERROR Build failed: Uses system libs: /lib/x86_64-linux-gnu/libz.so.1 /usr/lib/x86_64-linux-gnu/libffi.so.6
INFO Compiling cpython took 6 minutes 46 seconds
INFO Overall compilation took 6 minutes 57 seconds

What should I do to get a fully portable build? And could we document that in a step-by-step how-to guide?

Start with the portable-python build 3.10.9 entry point and reproduce the commands shown in the issue inside ubuntu:18.04. Trace why the resulting build reports /lib/x86_64-linux-gnu/libz.so.1 and /usr/lib/x86_64-linux-gnu/libffi.so.6 as system libraries. Done means a step-by-step how-to explains how to produce a fully portable Python build.