Add a note about moving configuration files

UPGRADE.md

@@ -5,6 +5,14 @@
 1. Support for Sylius 1.12 has been dropped, upgrade your application to [Sylius 1.13](https://github.com/Sylius/Sylius/blob/1.13/UPGRADE-1.13.md).
    or [Sylius 1.14](https://github.com/Sylius/Sylius/blob/1.14/UPGRADE-1.14.md).
 
+1. The configuration file has been moved from `@SyliusInvoicingPlugin/Resources/config/config.yml` to `@SyliusInvoicingPlugin/config/config.yaml`,
+   adjust the import in your end application.
+
+1. The routes configuration files have been moved:
+   - for Admin, from `@SyliusInvoicingPlugin/Resources/config/app/routing/admin_invoicing.yml` to `@SyliusInvoicingPlugin/config/admin_routes.yaml`
+   - for Shop, from `@SyliusInvoicingPlugin/Resources/config/app/routing/shop_invoicing.yml` to `@SyliusInvoicingPlugin/config/shop_routes.yaml`
+   adjust the routes in your end application.
+
 1. The deprecated method `Sylius\InvoicingPlugin\Entity\InvoiceInterface::orderNumber()` has been removed, 
    use `Sylius\InvoicingPlugin\Entity\InvoiceInterface::order()` instead.