Update wording on ParentRef field to require AllowedRoutes or Referen…

…ceGrant

Signed-off-by: Nick Young <nick@isovalent.com>

apis/v1beta1/shared_types.go

@@ -140,6 +140,13 @@ type CommonRouteSpec struct {
 	// case, the list of routes attached to those resources should also be
 	// merged.
 	//
+	// Note that for ParentRefs that cross namespace boundaries, the parent
+	// being referred to must have some mechanism to allow Routes to attach.
+	// Gateway has the AllowedRoutes field, for example. Any other resource
+	// being used as a parent across namespaces MUST either include an AllowedRoutes
+	// field or equivalent functionality, OR use a ReferenceGrant (if the spec
+	// can't have a field added).
+	//
 	// +optional
 	// +kubebuilder:validation:MaxItems=32
 	ParentRefs []ParentReference `json:"parentRefs,omitempty"`