[#143737725] Explain why we need to be supplied a CA keys stub file.
[#143737725] Explain why we need to be supplied a CA keys stub file.

Signed-off-by: Chunyi Lyu <0f8e751eae2b6087fa04691c2ff75f586389adcc@pivotal.io>

cloudfoundry/cf-deployment,emalm/cf-deployment,cloudfoundry/cf-deployment