Add a release note

Signed-off-by: Richard Wall <richard.wall@jetstack.io>

content/docs/release-notes/release-notes-1.12.md

@@ -23,3 +23,14 @@ authenticate to Vault.
 cert-manager now supports the `ingressClassName` field in the HTTP-01 solver. We
 recommend using `ingressClassName` instead of the field `class` in your Issuers
 and ClusterIssuers.
+
+### Liveness probe and healthz endpoint in the controller
+
+A healthz HTTP server has been added to the controller component.
+It serves a `/livez`  endpoint, which reports the health status of the leader election system.
+If the leader process has failed to renew its lease but has unexpectedly failed to exit,
+the `/livez` endpoint will return an error code and an error message.
+In conjunction with a new liveness probe in the controller Pod,
+this will cause the controller to be restarted by the kubelet.
+
+> 📖 Read more about this new feature in [Best Practice: Use Liveness Probes](../installation/best-practice.md#use-liveness-probes).