Fix codeblocks on main README

[jhdark]

Many of the code blocks are outdated, these need to be fixed and/or find a way to test them

[RemDelaporteMathurin]

I believe there is an action to test (with pytest) the code blocks in a readme

[RemDelaporteMathurin]

@jhdark there is this: https://github.com/nschloe/pytest-codeblocks

But last activity is 3 years ago