Moving all notebooks

[kolibril13]

I've now added the notebooks to the file index.rst, so that they will be recognized by the sphinx build.
The sphinx build was successful, and can now be seen here: https://simpleitk-notebooks--331.org.readthedocs.build/en/331/index.html

I've tried hard to keep the docs/ and the Python/ folder separate following this post:
https://stackoverflow.com/questions/10199233/can-sphinx-link-to-documents-that-are-not-located-in-directories-below-the-root
But I did not manage to accomplish it. Thus, I simply moved the Python folder into the docs/source folder
( e.g. Python/00_Setup.ipynb → docs/source/Python/00_Setup.ipynb )
EDIT: Linked issue: #330

[kolibril13]

Not the best idea, because tests are failing and less visibility, other attempt at:
#332

[kolibril13]

This is the way to go!
Closing it in favour of #333