Add note about the release image signature. Which was present until doc v4.7.

Author: trotro

modules/update-restricted.adoc

@@ -19,6 +19,11 @@ If you have a local OpenShift Update Service, you can update by using the connec
 
 * You mirrored the images for the new release to your registry.
 * You applied the release image signature ConfigMap for the new release to your cluster.
++
+[NOTE]
+====
+The release image signature config map allows the Cluster Version Operator (CVO) to ensure the integrity of release images by verifying that the actual image signatures match the expected signatures.
+====
 * You obtained the sha256 digest for your targeted release image.
 * You installed the OpenShift CLI (`oc`).
 * You paused all `MachineHealthCheck` resources.

updating/updating-restricted-network-cluster/restricted-network-update-osus.adoc

@@ -114,6 +114,11 @@ Before updating your cluster, confirm that the following conditions are met:
 
 * The Cluster Version Operator (CVO) is configured to use your locally-installed OpenShift Update Service application.
 * The release image signature config map for the new release is applied to your cluster.
++
+[NOTE]
+====
+The release image signature config map allows the Cluster Version Operator (CVO) to ensure the integrity of release images by verifying that the actual image signatures match the expected signatures.
+====
 * The current release and update target release images are mirrored to a locally accessible registry.
 * A recent graph data container image has been mirrored to your local registry.