Docs fallout

Author: flaper87

src/libcore/cell.rs

@@ -509,12 +509,13 @@ impl<'b, T> DerefMut for RefMut<'b, T> {
 ///
 /// ```rust
 /// use std::cell::UnsafeCell;
-/// use std::marker;
+/// use std::marker::Sync;
 ///
 /// struct NotThreadSafe<T> {
 ///     value: UnsafeCell<T>,
-///     marker: marker::NoSync
 /// }
+///
+/// unsafe impl<T> Sync for NotThreadSafe<T> {}
 /// ```
 ///
 /// **NOTE:** `UnsafeCell<T>` fields are public to allow static initializers. It