Update lab04.adoc

Adding a description of why we are adding imageContentSources

content/modules/ROOT/pages/lab04.adoc

@@ -149,6 +149,8 @@ The __pull secret__ that gets added to a disconnected installation's `install-co
 
 image::install-config-4.svg[initial config,width=600]
 
+We will be using what was generated by `oc-mirror` to ensure that the cluster uses our disconnected mirror for container images running on the [.highside]#highside# system.
+
 When `oc-mirror` is done uploading the OpenShift installation images into the `mirror-registry` it creates several __results files__.
 The contents of the `imageContentSourcePolicy.yaml` __result file__ must be added to the `install-config.yaml` __answer file__.
 
@@ -314,4 +316,4 @@ The OpenShift Installer (`openshift-install`) is specifically built for every ve
 
 This means that `openshift-install` version `{openshift_min_version}` will install OpenShift `{openshift_min_version}`.
 It also means you can't use `openshift-install` version `{openshift_min_version}` to install OpenShift `{openshift_max_version}`.
---
+--