OCPBUGS-43596:updates compute machine to include all platforms

Author: JoeAldinger

machine_management/user_infra/adding-bare-metal-compute-user-infra.adoc

@@ -6,11 +6,12 @@ include::_attributes/common-attributes.adoc[]
 
 toc::[]
 
-You can add more compute machines to your {product-title} cluster on bare metal.
+You can add more compute machines to your {product-title} cluster on bare metal or platform agnostic cluster.
 
 == Prerequisites
 
 * You xref:../../installing/installing_bare_metal/upi/installing-bare-metal.adoc#installing-bare-metal[installed a cluster on bare metal].
+* You xref:../../installing/installing_platform_agnostic/installing-platform-agnostic.adoc#installing-platform-agnostic[installed a cluster on any platform].
 * You have installation media and {op-system-first} images that you used to create your cluster. If you do not have these files, you must obtain them by following the instructions in the xref:../../installing/installing_bare_metal/upi/installing-bare-metal.adoc#installing-bare-metal[installation procedure].
 * If a DHCP server is available for your user-provisioned infrastructure, you have added the details for the additional compute machines to your DHCP server configuration. This includes a persistent IP address, DNS server information, and a hostname for each machine.
 * You have updated your DNS configuration to include the record name and IP address of each compute machine that you are adding. You have validated that DNS lookup and reverse DNS lookup resolve correctly.