Add term definitions in the scope of ReferrerStore and Verifier

[binbin-li]

What would you like to be added?

Current Oras Store might throw some errors wrapping up errors from Oras-go library, which requires knowledge on the OCI spec. However, beginners might not have enough context on those errors, especially the teminologies in the error message. We probably need to have a section in Store doc to define those common terms. We could just copy definitions from OCI spec, but it's better to provide some examples to help beginner understand it.

Terms might need to be defined:

• Blob
• Manifest
• Image
• Artifact
• Descriptor
• Digest
• Tag
• Subject
• Reference
• Referrers

The same thing applies to Verifier as well.

• Certificate
• Certificate chain
• Root/leaf/intermediate certificate
• Signature

Feel free to add more terms.

Anything else you would like to add?

No response

Are you willing to submit PRs to contribute to this feature?

• Yes, I am willing to implement it.