docs/spec: refer to v2beta2 doc for design details

Signed-off-by: Hidde Beydals <hidde@hhh.computer>

Author: hiddeco

docs/spec/README.md

@@ -51,7 +51,7 @@ trigger a Helm uninstall.
 Alerting can be configured with a Kubernetes custom resource that specifies a webhook address, and a
 group of `HelmRelease` resources to be monitored using the [notification-controller](https://github.com/fluxcd/notification-controller).
 
-The API design of the controller can be found at [helm.toolkit.fluxcd.io/v2beta1](./v2beta1/helmreleases.md).
+The API design of the controller can be found at [helm.toolkit.fluxcd.io/v2beta2](./v2beta2/helmreleases.md).
 
 ## Backward compatibility