Documentation consistency fixes

Author: balt-dev

library/alloc/src/collections/linked_list.rs

@@ -899,7 +899,7 @@ impl<T, A: Allocator> LinkedList<T, A> {
         self.pop_front_node().map(Node::into_element)
     }
 
-    /// Appends an element to the back of a list.
+    /// Adds an element to the back of a list.
     ///
     /// This operation should compute in *O*(1) time.
     ///

library/alloc/src/vec/mod.rs

@@ -2050,7 +2050,8 @@ impl<T, A: Allocator> Vec<T, A> {
     }
 
     /// Inserts an element at position `index` within the vector, shifting all
-    /// elements after it to the right.
+    /// elements after it to the right, and returning a reference to the new
+    /// element.
     ///
     /// # Panics
     ///