chore: add network mode annotation

Author: Kamil Przybyl

docs/albcm.md

@@ -105,6 +105,13 @@ spec:
               number: 80
 ```
 
+### Network Routing Mode
+The network routing mode determines how the ALB forwards external traffic to your applications within the cluster. Specifying this mode is mandatory. If omitted, your resource will be rejected by the validation webhook.
+
+You must set the `alb.stackit.cloud/network-mode` annotation on your IngressClass.
+
+Currently `NodePort` is the only supported mode. The ALB routes traffic to the cluster nodes, which then forward it to your pods. Future releases will introduce direct-to-pod routing as an additional mode. Setting `NodePort` now ensures your current configurations remain backwards compatible when new modes are added.
+
 ### WebSockets Support
 You can enable WebSocket support for your applications by adding a specific annotation to your Ingress resource. Note that in this initial release, enabling this annotation applies globally to all routing rules defined within that specific Ingress.
 
@@ -134,3 +141,4 @@ metadata:
   annotations:
     alb.stackit.cloud/web-application-firewall-name: "my-waf-config"
 ```
+