issue was closed, but discovered this feature doc was not added to the TOC in 2020

Author: swopebe

clusters/cluster_lifecycle/release_image_intro.adoc

@@ -8,3 +8,4 @@ Continue reading to learn more about release images:
 * xref:../cluster_lifecycle/release_images_specify.adoc#release-images-specify[Specifying release images]
 * xref:../cluster_lifecycle/release_image_connected.adoc#release-images-connected[Maintaining a custom list of release images while connected]
 * xref:../cluster_lifecycle/release_image_disconn.adoc#release-images-disconnected[Maintaining a custom list of release images while disconnected]
+* xref:../cluster_lifecycle/sync_release_image.adoc#sync-release-images[Synchronizing available release images]

clusters/main.adoc

@@ -38,6 +38,7 @@ include::cluster_lifecycle/release_image_intro.adoc[leveloffset=+3]
 include::cluster_lifecycle/release_images_specify.adoc[leveloffset=+4]
 include::cluster_lifecycle/release_image_connected.adoc[leveloffset=+4]
 include::cluster_lifecycle/release_image_disconn.adoc[leveloffset=+4]
+include::cluster_lifecycle/sync_release_image.adoc[leveloffset=+4]
 include::cluster_lifecycle/cim_intro.adoc[leveloffset=+3]
 include::cluster_lifecycle/cim_enable.adoc[leveloffset=+4]
 include::cluster_lifecycle/cim_enable_aws.adoc[leveloffset=+4]