example non-cloned apply fails due to missing tree ref in URL

[dlbewley]

RHACM offers this instruction to apply without cloning

oc apply -k https://github.com/redhat-cop/gitops-catalog/advanced-cluster-management/operator/overlays/<channel>

This does not work. Needs to be

oc apply -k https://github.com/redhat-cop/gitops-catalog/advanced-cluster-management/operator/overlays/<channel>\?ref\=main

This can be tested as:

oc kustomize https://github.com/redhat-cop/gitops-catalog/advanced-cluster-management/operator/overlays/release-2.12\?ref\=main

This is probably found in other READMEs. Just filing an issue before I forget again.