fix update upselling rule

README.md

@@ -34,4 +34,7 @@ http://localhost/api/upselling/documentation
 4) Create a upselling rule and include product id, category id, brand id, price range, discount range, and quantity range.
 
 
-```
+```
+
+# Upselling Method
+> Base use NexaMerchant Cart rule, and use it for cost the price for order