REFACTOR: move the example `.nu` scripts

[amtoine]

Related to https://github.com/fdncred/nufmt/issues/1.

This won't close the issue, it's just one of the points :yum:

This PR simply:

• moves the .nu scripts to examples/
• mention them with disclaimers in the readme

Warning
i think we should wait for #2 to be merged and then merge here the new name :yum:

[amtoine]

as #2 has been merged, i've fixed the conflicts between this branch and the new main => i think it's ready for review!

[fdncred]

good enough