Enhance documentation for oras-go v2

[Wwwsylvia]

While we already have documentation covering the general concepts of ORAS on oras.land and detailed API specifications available on pkg.go.dev, users may still encounter challenges when trying to use oras-go v2 in their projects.

To enhance clarity and usability, we should consider the following improvements:

• Refine README.md to include a brief summary of the library #813
• Add documentation to clarify common concepts in oras-go v2 #814
• Add documentation about the modeling of OCI artifacts #815
• Add a quickstart tutorial #816
• Add more practical E2E examples #817
• Review existing examples and fix any issues found #818

Related issue: oras-project/oras-www#67

Feel free to share additional ideas or suggestions in the comments! Let’s make the documentation more accessible and user-friendly. 💡

[Wwwsylvia]

TODO: break down to more granular tasks

[shizhMSFT]

It would be better if we have tutorials beyond examples like a tour of go.

We don't need a full website and we can start with just a markdown file like the gin tutorial (rendered page).

[FeynmanZhou]

@Wwwsylvia I received a feedback about having the subject/referrer relationship made clear in the oras-go docs and add example code of how to add a subject using PackManifest would be super helpful.

[Wwwsylvia]

Here are some tasks I'm currently considering:

• Refine README.md to include a brief summary of the library.
• 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 to choose the appropriate content store.
• 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 and ExtendedCopy.
• Add a quickstart tutorial similar to the Gin tutorial (rendered page), including:
  • How to import oras-go v2.
  • How to write basic code using oras-go v2 APIs.
  • How to run the code.
• 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 to a remote repository.
• Review existing examples and fix any issues found