Highlighted repo as Optional

Author: amolnar-rh

modules/ztp-precaching-downloading-artifacts.adoc

@@ -258,7 +258,7 @@ You can customize the `ImageSetConfiguration` CR in the following ways:
 <3> Defines the {rh-rhacm} version.
 <4> Defines the MCE version.
 <5> Defines the folder where you want to download the images on the disk.
-<6> Defines the repository where you store your additional images. These images are downloaded and pre-cached on the disk.
+<6> Optional. Defines the repository where you store your additional images. These images are downloaded and pre-cached on the disk.
 <7> Specifies pre-caching the Operators included in the DU configuration.
 <8> The `--generate-imageset` argument generates the `ImageSetConfiguration` CR only, which allows you to customize the CR.