added a note explaining why routerKeyFn was added

pkg/router/controller/factory/factory.go

@@ -57,6 +57,9 @@ func NewDefaultRouterControllerFactory(oc osclient.RoutesNamespacer, kc kclients
 	}
 }
 
+// routerKeyFn comes from MetaNamespaceKeyFunc in vendor/k8s.io/kubernetes/pkg/client/cache/store.go.
+// It was modified and added here because there is no way to know if an ExplicitKey was passed before 
+// adding the UID to prevent an invalid state transistion if deletions and adds happen quickly.
 func routerKeyFn(obj interface{}) (string, error) {
 	if key, ok := obj.(cache.ExplicitKey); ok {
 		return string(key), nil