Inform when the feature was introduced

Author: IKarbowiak

docs/developer/checkout/address.mdx

@@ -426,6 +426,11 @@ The fields for shipping and billing addresses will be normalized (if needed) on
 :::
 
 ## Customer Address Saving Strategies
+
+:::info
+This feature was introduced in **Saleor 3.21**.
+:::
+
 Address updates allow configuring the address-saving strategy for both shipping and billing addresses.
 This setting determines whether the shipping or billing address should be saved in the customer's address book.
 It applies only when the checkout is completed by a logged-in user.

docs/developer/order/address.mdx

@@ -3,6 +3,11 @@ title: Shipping and Billing
 ---
 
 ## Customer Address Saving Strategies
+
+:::info
+This feature was introduced in **Saleor 3.21**.
+:::
+
 Address updates allow configuring the address-saving strategy for both shipping and billing addresses.
 This setting determines whether the shipping or billing address should be saved in the customer's address book.
 This setting takes effect only when a draft order is completed for an existing user.