Improve the document for new users to understand quickly that Cosign supports blobs signing

[suzuki-shunsuke]

Thank you for your great project.
I have a feedback about the document about Cosign.

Cosign supports not only containers but also standard files and blobs (or binary large objects).

https://docs.sigstore.dev/cosign/working_with_blobs

But I misunderstood Cosign supports only containers, because the repository description and the top of README and official document describe only containers.

repository description

Container Signing

README

Container Signing, Verification and Storage in an OCI registry.

Official document: https://docs.sigstore.dev/cosign/overview

Cosign supports container signing, verification, and storage in an OCI registry.

I know there is a document about blobs signing, but users may miss the document.

So I think we should improve the document so that new users can understand quickly that Cosign supports blobs signing.

What do you think?

[suzuki-shunsuke]

Oh, the issue label is inappropriate.
Could you remove the enhancement label and add the documentation label?

[dlorenc]

All set!