Auto merge of rust-lang#5312 - joshtriplett:wildcard-prelude-document…

…ation, r=flip1995

Document that wildcard_imports doesn't warn about `use ...::prelude::*;`

changelog: Improve [`wildcard_imports`] documentation

clippy_lints/src/wildcard_imports.rs

@@ -43,6 +43,10 @@ declare_clippy_lint! {
     ///
     /// This can lead to confusing error messages at best and to unexpected behavior at worst.
     ///
+    /// Note that this will not warn about wildcard imports from modules named `prelude`; many
+    /// crates (including the standard library) provide modules named "prelude" specifically
+    /// designed for wildcard import.
+    ///
     /// **Known problems:** If macros are imported through the wildcard, this macro is not included
     /// by the suggestion and has to be added by hand.
     ///