docs: docs for next release (#14110)

www/apps/user-guide/app/orders/exchanges/page.mdx

@@ -57,6 +57,8 @@ To create an order exchange:
         - The shipping method's cost is added to the exchange total. To edit its cost:
             - Click the <InlineIcon Icon={PencilSquare} alt="edit" /> icon next to the Outbound Shipping total.
             - Enter the new cost in the input shown.
+    - If the order has promotions, you can enable the "Carry over promotions" toggle to apply the same promotions to the exchange's items.
+        - You can only carry over fixed promotions with `EACH` allocation type, or percentage promotions of `EACH` or `ACROSS` allocation types. Promotions are carried over to outbound items only.
     - If you want the customer to receive a notification that an exchange has been created, check the “Send notifications” toggle.
 5. Once done, click on the "Confirm Exchange" button, then confirm the action by clicking the "Continue" button in the pop-up.