Add an example aws command for querying valid AMI images

The current WMCO docs for AWS only mention "Windows Server 2019,
version 1809 Long-Term Servicing Channel (LTSC)" as a supported
Windows version. For newcomers to Windows containers and AWS it's hard
to figure out the right AMI to use.

The example command added in this pull request is actually taken from
upstream:

https://github.com/openshift/windows-machine-config-operator/blob/master/hack/machineset.sh#L82

Author: tosmi

windows_containers/creating_windows_machinesets/creating-windows-machineset-aws.adoc

@@ -12,7 +12,14 @@ You can create a Windows `MachineSet` object to serve a specific purpose in your
 == Prerequisites
 
 * You installed the Windows Machine Config Operator (WMCO) using Operator Lifecycle Manager (OLM).
-* You are using a supported Windows Server as the operating system image. 
+* You are using a supported Windows Server as the operating system image.
++
+Use the following `aws` command to query valid AMI images:
++
+[source,terminal]
+----------
+aws ec2 describe-images --region <aws region name> --filters "Name=name,Values=Windows_Server-2019*English*Full*Containers*" "Name=is-public,Values=true" --query "reverse(sort_by(Images, &CreationDate))[*].{name: Name, id: ImageId}" --output table
+----------
 
 include::modules/machine-api-overview.adoc[leveloffset=+1]
 include::modules/windows-machineset-aws.adoc[leveloffset=+1]