Note for future guidelines to showcase `NonZero<T>`

[PLeVasseur]

Creating an issue so this doesn't get lost:

In the future, I'd also like to have a more thorough showcase of NonZero. One of its main advantages is that one can create such a divisor and afterwards use it with / and % as many times as needed without any runtime performance penalty - in fact, it actually increases the performance as the compiler can elide the "is the divisor zero?" runtime checks that lead to panics. But! Let's leave that example for a later revision. For whenever we're able to have multiple examples

cc @felix91gr