Add message to indicate that v1 env subnet cannot be delegated

Author: chinadragon0515

articles/container-apps/networking.md

@@ -158,6 +158,8 @@ Different environment types have different subnet requirements:
 
 - `/23` is the minimum subnet size required for virtual network integration.
 
+- Your subnet must NOT be delegated to any services.
+
 - The Container Apps runtime reserves a minimum of 60 IPs for infrastructure in your VNet. The reserved amount may increase up to 256 addresses as apps in your environment scale.
 
 - As your apps scale, a new IP address is allocated for each new replica.