Update the docs to reflect get_item instead of items

README.markdown

@@ -127,7 +127,7 @@ View the items included in a plan...
 
 Set an item's quantity (if the item is attached to a customer):
 
-    >>> item = customer.items[0]
+    >>> item = customer.get_item("The Item's Code")
     >>> item.quantity = 5
     >>> item.save()
     >>>
@@ -137,4 +137,4 @@ Set an item's quantity (if the item is attached to a customer):
     >>> item.quantity = 5
     >>> item.save()
     pycheddar.exceptions.ValidationError: Items may only have their quantity altered if they are directly attached to a customer.
-
+