Add a pre-commit git hook to prevent commit of a notebook with executed cells within

Closes #2

See merge request !7

Script to check notebooks: remove the she-bang and add two arguments to circumvent an issue with UTF 8 encoding (fix suggested there: https://www.journaldunet.fr/web-tech/developpement/1441055-corriger-l-erreur-unicodedecodeerror-utf-8-codec-can-t-decode-byte-0xff-in-position-0-invalid-start-byte/).

#2 Use sys.exit() rather than exit() in Python script, following the suggestion fron Laurent Steff in its review of MR ctest -I 45,45,1 -V.

This reverts merge request !4

Update readme to add documentation VSCode

See merge request !4

Refactor a bit the way Docker images are used; the third party warnings are now a full-fledged demo.