Link directly to OpenAPI schema. (#2436)

* Link directly to OpenAPI schema.

* Update validation.go

Author: etefera

pkg/api/kptfile/v1/validation.go

@@ -212,8 +212,7 @@ func IsKRM(n *yaml.RNode) error {
 	return nil
 }
 
-// isKustomization determines if given YAML is a kustomization file
-// or a kustomization resource.
+// isKustomization determines if given YAML is a kustomization file or resource.
 func isKustomization(n *yaml.RNode) bool {
 	resourcePath, _, err := kioutil.GetFileAnnotations(n)
 	if err == nil {

site/reference/schema/kptfile/README.md

@@ -1,4 +1,4 @@
 # Kptfile
 
-See
-[definition here](https://github.com/googlecontainertools/kpt/blob/next/pkg/api/kptfile/v1/types.go#L41)
+Grab the OpenAPI
+[schema here](https://kpt.dev/reference/schema/kptfile/kptfile.yaml)