Add headings to address build failures

Author: aneta-petrova

guides/doc-Configuring_virt-who_VM_Subscriptions/master.adoc

@@ -7,9 +7,13 @@ include::common/header.adoc[]
 = {ConfiguringVMSubscriptionsDocTitle}
 
 ifdef::foreman-deb[]
+== Katello plugin required
+
 You cannot use the virt-who plugin because it requires the Katello plugin, which is not supported on Debian or Ubuntu.
 endif::[]
 ifdef::foreman-el[]
+== Katello plugin required
+
 You cannot use the virt-who plugin without the Katello plugin.
 endif::[]