Add a tiny end-to-end example to README/docs

I was looking through Spec Kit and the tagline “Define what to build before building it — with any AI coding agent” makes the goal clear, but I had a little trouble forming a mental model of the actual workflow from the README alone.

It would help newcomers to include a very small example near the Get Started section: a short spec file or PRD fragment, the command/template used to process it, and what the next artifact looks like when handed to an agent like Copilot. Even a contrived example like “add a /health endpoint” would make the boundaries clearer.

If a fuller example already lives in docs or an examples directory, a direct link from the README would still be useful. The main benefit is reducing the blank-page problem for people trying to map spec-driven development onto their own repo.

Start at the README's Get Started section and check whether a fuller example already exists in the docs or examples directory. Add a small end-to-end example covering a spec or PRD fragment, the command or template used, and the resulting artifact for an AI coding agent, or link to an existing example; done means newcomers can follow the workflow without the blank-page problem.

索引モデルが issue の本文から書いたものです。