update doc

[bubunyo]

update doc

[Copilot]

Pull request overview

Updates the README usage documentation to match the current BuildGraph CLI entrypoint and analyze output behavior.

Changes:

• Update installation and local build commands to use the module root (go install github.com/bubunyo/buildgraph@latest, go build .).
• Refresh buildgraph analyze examples to reflect text as the default format and document json/dot formats.
• Adjust CI baseline persistence description wording (artifact naming examples).

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[Copilot]

This section now states that each branch gets its own baseline artifact (e.g. buildgraph-baseline-main). That naming scheme conflicts with the repository’s other documentation/spec, which still references a single buildgraph-baseline artifact name in the CI examples (see SPEC.md around the GitHub Actions example). Please align the docs (either make the README wording more generic/configurable, or update the other docs/examples) to avoid confusing users about the expected artifact name(s).

Suggested change

The baseline artifact is uploaded at the end of each successful run and downloaded at the start of the next. Each branch gets its own artifact (e.g. `buildgraph-baseline-main`, `buildgraph-baseline-feature-foo`) so branches don't interfere with each other. On the very first run no artifact exists yet — BuildGraph treats all functions as new and returns all services in `services_to_build`, so a cold start is always safe.

The baseline artifact is uploaded at the end of each successful run and downloaded at the start of the next. The exact artifact name and how it is scoped (single shared artifact vs. per-branch artifacts) are controlled by your CI workflow configuration, so that branches can be isolated if desired. On the very first run no artifact exists yet — BuildGraph treats all functions as new and returns all services in `services_to_build`, so a cold start is always safe.