DEVDOCS-5572: [Update] add notes about concurrent requests

reference/carts.v3.yml

@@ -288,6 +288,8 @@ paths:
         Overriding a product’s `list_price` will make that item ineligible for V3 product level promotions.
 
         If a product has modifiers, omit the `variant_id` and instead use the `option_selections` array to describe both the **variant** and the **modifier** selections.
+
+         We recommend firing cart requests individually to prevent lost updates or duplicate requests. Concurrent cart API requests are not supported.
       parameters:
         - name: include
           in: query
@@ -395,6 +397,8 @@ paths:
         `custom_items` cannot be updated via the API at this time. To update your cart, add a new updated custom item and delete the outdated one. If your cart contains only one line item, perform the add operation before the delete operation.
 
         Deleting all line items from the cart will invalidate the cart. 
+
+        We recommend firing cart requests individually to prevent lost updates or duplicate requests. Concurrent cart API requests are not supported.
       parameters:
         - name: include
           in: query