Update Readme

[fsimonis]

This PR updates the Readme and adds a __main__.py to the package to get nuitka working again.

Note that compiling the script with nuitka leads to an error in vtk. So far I couldn't find a way to fix this.

When I run python -m nuitka --follow-imports --python-flag=-m ccx2paraview (same for --standalone) and then run the result I get :

$ ./ccx2paraview.bin
Traceback (most recent call last):
  File "/.../ccx2paraview/ccx2paraview/__main__.py", line 1, in <module>
    from . import cli

  File "/.../ccx2paraview/ccx2paraview/cli.py", line 13, in <module ccx2paraview.cli>
    from .common import Converter

  File "/.../ccx2paraview/ccx2paraview/common.py", line 21, in <module ccx2paraview.common>
    import vtk

  File "/.../venv/lib/python3.11/site-packages/vtk.py", line 47, in <module vtk>
    from vtkmodules.vtkRenderingMatplotlib import *

ImportError: /.../ccx2paraview/venv/lib/python3.11/site-packages/vtkmodules/libvtkPythonInterpreter-9.2.so: undefined symbol: Py_RunMain

[imirzov]

Since now we do not need to create binaries at all.