Rollup merge of rust-lang#62656 - RalfJung:contains-no-own, r=Dylan-DPC

explain how to search in slice without owned data

Cc rust-lang#62367

src/libcore/slice/mod.rs

@@ -1263,6 +1263,15 @@ impl<T> [T] {
     /// assert!(v.contains(&30));
     /// assert!(!v.contains(&50));
     /// ```
+    ///
+    /// If you do not have an `&T`, but just an `&U` such that `T: Borrow<U>`
+    /// (e.g. `String: Borrow<str>`), you can use `iter().any`:
+    ///
+    /// ```
+    /// let v = [String::from("hello"), String::from("world")]; // slice of `String`
+    /// assert!(v.iter().any(|e| e == "hello")); // search with `&str`
+    /// assert!(!v.iter().any(|e| e == "hi"));
+    /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn contains(&self, x: &T) -> bool
         where T: PartialEq