Lixia (Sylvia) Lei

We should review all existing examples on [pkg.go.dev](https://pkg.go.dev/oras.land/oras-go/v2) and fix any issues like: - Unclear code - Confusing example naming

We should add E2E examples on: - How to attach a blob to an existing artifact in a remote repository. - How to push an artifact along with its referrers...

We should add documentation about the modeling of OCI artifacts, including: - Visualization of the artifact graph model. - The relationship between `Predecessors` and `Referrers`. - The difference between `Copy`...

We should add documentation to clarify common concepts in oras-go v2, including: - The concept of Target and content store. - A summary for each built-in content store. - How...