Adding more information about the behavior of Arc/Rc

when you perform a clone() call.

src/liballoc/arc.rs

@@ -94,6 +94,9 @@ use heap::deallocate;
 /// With simple pipes, without `Arc`, a copy would have to be made for each
 /// task.
 ///
+/// When you clone an `Arc<T>`, it will create another pointer to the data and
+/// increase the reference counter.
+///
 /// ```
 /// # #![feature(alloc, core)]
 /// use std::sync::Arc;

src/liballoc/rc.rs

@@ -431,7 +431,8 @@ impl<T> Clone for Rc<T> {
 
     /// Makes a clone of the `Rc<T>`.
     ///
-    /// This increases the strong reference count.
+    /// When you clone an `Rc<T>`, it will create another pointer to the data and
+    /// increase the strong reference counter.
     ///
     /// # Examples
     ///