The contributing notes for the nu website is missing a style guide

It would also be nice to add some style guides for contributing to the book. Currently the style of e.g. code examples is a bit inconsistent. For example:

1. Code examples should use the nu formatting as in ```nu , currently this is not very consistent as I see none, bash, sh, nu and nushell used. I think it would be nice to have these consisten.
2. Another that might be nice is to use a consistent style for output formating of tables. E.g. "examples of table output should use rounded corners" (don't actually mean it needs to be rounded, just that we would use a consistent styling"

Commencez par localiser les notes de contribution du site web et le contenu du livre qu’elles couvrent. Documentez des libellés cohérents pour les blocs de code Nu et un style unique pour la sortie des tableaux, puis vérifiez les exemples environnants afin de vous assurer que les indications sont claires et applicables.