Add some release notes

Author: Martin Jackson

Changes.md

@@ -50,3 +50,5 @@
 * Use api_version for Route queries when discovering credentials for AAP instance.
 * Update common.
 * Update deploy_kubevirt_worker.yml Ansible playbook to copy securityGroups and blockDevices config from first machineSet. Tag naming schemes changed from OCP 4.15 to 4.16; this method ensures forward and backward compatibility.
+* Remove ODF overrides from OCP 4.12/3 that force storageClass to gp2; all released versions should use gp3-csi now.
+* Include overrides for OCP 4.12 and OCP 4.13 to use the older `ocs-storagecluster-ceph-rbd` storageClass.