Document that programmer can't use generic NonZero #142966
Description
Location
std::num::NonZero in the standard library rustdocs
Summary
Since #120257, we have had, on stable, NonZero<T>. But really it's NonZero<T: unnameable> (because ZeroablePrimitive is perma-unstrable).
The effect is that the programmer can talk about NonZero<SomeConcreteType>, but unlike most other generics in the standard library, they can't impl<T:...> MyTrait for NonZero<T>. (That's point 5 in "Other surface area not being proposed for stabilization right now" in #120257 (comment).)
It would be good if this were explicitly mentioned in the docs for NonZero. That might save people setting out to try to do the impossible.