Description of problem:

When going through the instructions under "Creating RHCOS machines using an ISO image" I noticed some areas that are incomplete

Ask user to change "<architecture>" string to their cluster's architecture 

Step 4 has the command: 

COS_VHD_ORIGIN_URL=$(oc -n openshift-machine-config-operator get configmap/coreos-bootimages -o jsonpath='{.data.stream}' | jq -r '.architectures.<architecture>.artifacts.metal.formats.iso.disk.location')

which requires the user to replace "<architecture>" with one of our supported architectures which can be found with this command:

# oc -n openshift-machine-config-operator get configmap/coreos-bootimages -o jsonpath='{.data.stream}' | jq -r '.architectures | keys'
[
  "aarch64",
  "ppc64le",
  "s390x",
  "x86_64"
] 

We should be explicit about telling the user to do this.

Ignition digest hash is never computed

Step 7 says "... <digest> is the Ignition config file SHA512 digest obtained in a preceding step." but we do not have a step that computes the digest