implementations: adding the C and Rust libraries
implementations: adding the C and Rust libraries

having seen #895, it's worth ensuring these other languages are listed
implementations

Signed-off-by: Vincent Batts <d01a4772f0cffd3f005a7d7f01c59cd104c7a5fe@hashbangbash.com>

opencontainers/image-spec,opencontainers/image-spec