config: address feedback from wking and
config: address feedback from wking and

- use correct indentation for sub lists
- address some missing OPTIONAL tags
- random formatting issues.

Thanks @coolljt0725 and @wking for the review.

Signed-off-by: Brandon Philips <74d2b51265fa19d338eb593a7555ec2b932e59c0@coreos.com>

jonboulle/image-spec,opencontainers/image-spec,jonboulle/image-spec,mattspencer-arm/image-spec,vbatts/oci-image-spec,vbatts/oci-image-spec,mattspencer-arm/image-spec,opencontainers/image-spec