Update the doc for std::prelude to the correct behavior

[poliorcetics]

Fixes #64686.

One line change to ensure the docs are correct about the behavior of the compiler when insertingstd::prelude::v1.

I don't think examples are necessary but I can add some (especially those from the original issue) if needed.

[rust-highfive]

r? @sfackler

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[ehuss]

I don't think this is correct.

Name resolution works through a chain of lookups. For example, it will roughly look in order:

1. local variables
2. items in unnamed blocks
3. items in the current module
4. crate names in the "extern prelude"
5. standard library prelude
6. language prelude (built-in types)

where each one can shadow the one below it. I don't think there is an equivalent way to express this through Rust code. Also std arrives in the extern prelude, not the library prelude (and the extern prelude contains a bunch of other things). I personally would just remove the "On a technical level..." section since it is wrong, and I think it is somewhat distracting to explain the details. All the reader needs to know is that the prelude items are implicitly in scope everywhere.

[sfackler]

@bors r+ rollup

[bors]

📌 Commit 8f0bd5f has been approved by sfackler