OSDOCS-15331 OSUS single stream release additional text

Author: cbippley

modules/update-service-overview.adoc

@@ -18,6 +18,10 @@ keep your cluster up to date with the most recent compatible components.
 
 To allow the OpenShift Update Service to provide only compatible updates, a release verification pipeline drives automation. Each release artifact is verified for compatibility with supported cloud platforms and system architectures, as well as other component packages. After the pipeline confirms the suitability of a release, the OpenShift Update Service notifies you that it is available.
 
+The OpenShift Update Service (OSUS) supports a single-stream release model, where only one release version is active and supported at any given time. When a new release is deployed, it fully replaces the previous release.
+
+The updated release provides support for upgrades from all {product-title} versions starting after 4.8 up to the new release version.
+
 [IMPORTANT]
 ====
 The OpenShift Update Service displays all recommended updates for your current cluster.  If an update path is not recommended by the OpenShift Update Service, it might be because of a known issue with the update or the target release.