Document the shipment mail and notify_customer

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -197,7 +197,8 @@ $order = $user->orders()->create([
 ```
 
 Once a paid order is sent, create a shipment. Anikeen ID adds its delivery note to the user's
-order documents (with the tracking link) and sends `order.shipped` to your webhook endpoints.
+order documents (with the tracking link), mails it to the user (`'notify_customer' => false` if
+your shop sends its own mail) and sends `order.shipped` to your webhook endpoints.
 Without `items`, everything physical that is left is shipped; partial deliveries name the items:
 
 ```php

src/Id/Resources/Shipments.php

@@ -27,11 +27,14 @@ class Shipments extends BaseCollection
      *     tracking_url?: string,
      *     note?: string,
      *     shipped_at?: string,
+     *     notify_customer?: bool,
      *     items?: array<array{order_item_id: string, units?: float|int|string}>
      * } $attributes
      *   - carrier:         e.g. "DHL"
      *   - tracking_url:    http(s) link to track the parcel, shown to the user
      *   - shipped_at:      when it was sent (default: now, not in the future)
+     *   - notify_customer: Anikeen ID mails the user with the delivery note (default true);
+     *                      false if your shop sends its own mail
      *   - items:           physical items of the order and how many of them (default: all left)
      *
      * Errors (ResourceException with the HTTP status): 409 when the order isn't paid or nothing