MGMT-19109: Add note to IBI standalone docs about machineNetwork req

Author: amolnar-rh

modules/ibi-create-standalone-config-iso.adoc

@@ -38,6 +38,7 @@ $ mkdir ibi-config-iso-workdir <1>
 
 .. Create a YAML file that defines the `install-config` manifest:
 +
+--
 .Example `install-config.yaml` file
 [source,yaml]
 ----
@@ -72,6 +73,15 @@ pullSecret: '{"auths":{"<your_pull_secret>"}}}'
 sshKey: 'ssh-rsa <your_ssh_pub_key>'
 ----
 
+[IMPORTANT]
+====
+If your cluster deployment requires a proxy configuration, you must do the following:
+
+* Create a seed image from a seed cluster featuring a proxy configuration. The proxy configurations do not have to match.
+* Configure the machineNetwork field in your installation manifest.
+====
+--
+
 .. Save the file in your working directory. 
 
 . Optional. Create a configuration template in your working directory by running the following command: