add comments to common/iso_config.go from docs
add comments to common/iso_config.go from docs

dave2/packer,dave2/packer,paulmey/packer,pecigonzalo/packer,grubernaut/packer,ricardclau/packer,ricardclau/packer,ricardclau/packer,mitchellh/packer,timsutton/packer,timsutton/packer,hashicorp/packer,timsutton/packer,ricardclau/packer,timsutton/packer,hashicorp/packer,dave2/packer,pecigonzalo/packer,mitchellh/packer,grubernaut/packer,ricardclau/packer,hashicorp/packer,rnaveiras/packer,paulmey/packer,mitchellh/packer,grubernaut/packer,pecigonzalo/packer,rnaveiras/packer,ricardclau/packer,rnaveiras/packer,timsutton/packer,rnaveiras/packer,grubernaut/packer,paulmey/packer,rnaveiras/packer,hashicorp/packer,rnaveiras/packer,mitchellh/packer,mitchellh/packer,dave2/packer,paulmey/packer,grubernaut/packer,dave2/packer,timsutton/packer,dave2/packer,paulmey/packer,paulmey/packer,pecigonzalo/packer,grubernaut/packer