Add custom resource quota example (#14492)

content/en/docs/concepts/policy/resource-quotas.md

@@ -136,6 +136,9 @@ Here is an example set of resources users may want to put under object count quo
 * `count/cronjobs.batch`
 * `count/deployments.extensions`
 
+The 1.15 release added support for custom resources using the same syntax.
+For example, to create a quota on a `widgets` custom resource in the `example.com` API group, use `count/widgets.example.com`.
+
 When using `count/*` resource quota, an object is charged against the quota if it exists in server storage.
 These types of quotas are useful to protect against exhaustion of storage resources.  For example, you may
 want to quota the number of secrets in a server given their large size.  Too many secrets in a cluster can