[Doc] Add a FEATURE.md or USER_STORY.md

• Tells the end-dev how we turn a user story into a feature, the ToC looks like this:
  • First, explain why it doesn't work today, why we need a change
  • Write 3+ user stories on how the end-dev would use this feature, one of them is the original ask
  • Converting user story into a feature, is a work of generalization
    • Generalize the variations across these user stories into a feature
    • The feature may not perfectly fit the original user story
      • Not perfect fit means, we may upset the original asker
      • Be sympathy and explain how the new feature can do better and farther than his ask
  • Verify the generalized feature works on these 3 user stories, probably in test page(s) to protect the investment and keep the promise
  • Think 2+ new user stories that this feature could empower
    • How far can we carry this feature farther?
• Link this doc to CONTRIBUTING.md

[feature-request]

Create FEATURE.md or USER_STORY.md following the requested user-story, generalization, verification, and future-use-case sections, then link it from CONTRIBUTING.md. Start by reading CONTRIBUTING.md to match the project's contribution guidance; done means the new process is understandable and the link works.