Added note about security implications of enabling IP forwarding

site/kubernetes/kube-addon.md

@@ -306,7 +306,8 @@ UDP connection from 10.32.0.7:56648 to 10.32.0.11:80 blocked by Weave NPC.
 - IP forwarding must be enabled on each node, in order for pods to
   access Kubernetes services or other IP addresses on another
   network. Check this with `sysctl net.ipv4.ip_forward`; the result
-  should be `1`.
+  should be `1`. (Be aware that there can be security implications of
+  enabling IP forwarding)
 
 ## <a name="configuration-options"></a> Changing Configuration Options