add CEL Playground link

Author: matheusfm

content/en/docs/reference/access-authn-authz/validating-admission-policy.md

@@ -67,6 +67,10 @@ The following is an example of a ValidatingAdmissionPolicy.
 to validate the request. If an expression evaluates to false, the validation check is enforced
 according to the `spec.failurePolicy` field.
 
+{{< note >}}
+You can quickly test CEL expressions in [CEL Playground](https://playcel.undistro.io).
+{{< /note >}}
+
 To configure a validating admission policy for use in a cluster, a binding is required.
 The following is an example of a ValidatingAdmissionPolicyBinding.:
 

content/en/docs/tasks/extend-kubernetes/custom-resources/custom-resource-definitions.md

@@ -849,6 +849,10 @@ The CronTab "my-new-cron-object" is invalid:
 * spec: Invalid value: map[string]interface {}{"maxReplicas":10, "minReplicas":0, "replicas":20}: failed rule: self.replicas <= self.maxReplicas
 ```
 
+{{< note >}}
+You can quickly test CEL expressions in [CEL Playground](https://playcel.undistro.io).
+{{< /note >}}
+
 Validation rules are compiled when CRDs are created/updated.
 The request of CRDs create/update will fail if compilation of validation rules fail.
 Compilation process includes type checking as well.