Add an example to Wrapping's documentation.

src/libcore/num/mod.rs

@@ -37,6 +37,17 @@ use slice::SliceExt;
 /// `wrapping_add`, or through the `Wrapping<T>` type, which says that
 /// all standard arithmetic operations on the underlying value are
 /// intended to have wrapping semantics.
+///
+/// # Examples
+///
+/// ```
+/// use std::num::Wrapping;
+///
+/// let zero = Wrapping(0u32);
+/// let one = Wrapping(1u32);
+///
+/// assert_eq!(std::u32::MAX, (zero - one).0);
+/// ```
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Default, Hash)]
 pub struct Wrapping<T>(#[stable(feature = "rust1", since = "1.0.0")] pub T);