Adds a release note to callout s390x and ppc64 for OMR

Author: Steven Smith

modules/mirror-registry-release-notes.adoc

@@ -89,6 +89,8 @@ New installations use SQLite by default. Before upgrading to version 2.0, see "U
 
 * A new feature flag, `--sqliteStorage` has been added. With this flag, you can manually set the location where SQLite database data is saved.
 
+* _Mirror registry for Red{nbsp}Hat OpenShift_ is now available on {ibm-power-title} and {ibm-z-title} architectures (`s390x` and `ppc64le`).
+
 [id="mirror-registry-release-notes-1-3_{context}"]
 == Mirror registry for Red{nbsp}Hat OpenShift 1.3 release notes