Improved Readme

Manually merged https://github.com/Crinsane/LaravelShoppingcart/pull/311

src/Cart.php

@@ -580,6 +580,8 @@ class Cart
             'identifier' => $identifier,
             'instance'   => $this->currentInstance(),
             'content'    => serialize($content),
+            'created_at' => date('Y-m-d H:i:s'),
+            'updated_at' => date('Y-m-d H:i:s')
         ]);
 
         $this->events->fire('cart.stored');