Updated readme for order edit

Author: zkimffm

README.md

@@ -360,10 +360,8 @@ Magento::api('orders')->show($orderId);
 Updates an order specified by the entity id within the $body:
 ```php
 $body = [
-    'entity' => [
         'entity_id' => '', // required
         // ... attributes to update
-    ]
 ];
 Magento::api('orders')->edit($body);
 ```