docs: explain the one-time update bootstrap

[justinhelmer]

Explain that automatic updates start in CLI 0.2.50 and that older installs need one manual update through their existing install channel.

This README-only clarification provides a small patch release so the published 0.2.50 updater can be validated against a newer public version. No runtime code changes.

Validation: wording matches the v0.2.50 release boundary; git diff --check passed. Docs-only; no new behavior tests apply. The normal PR and release checks remain required before publication.

[polylane]

Note

Production impact unlikely.

Documentation, test, or CI-only change; nothing that runs in production is affected.

_{Polylane analysed c099943 for production impact. You can ask follow-ups by mentioning @polylane in a comment.}

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[coreplane-switchboard]

No verdict submitted — not approving.

Reviewed at c099943.

For agents

Full review

Review blocked: the required exact-head check aborted without returning a result, so I could not confirm c09994356a880608315c454c81a93eedd55ad985. No findings or verdict were submitted; no changes were made.

[coreplane-switchboard]

LGTM: no issues found

Reviewed at c099943.

For agents

Rationale: docs-only; no local checks apply. The clarification matches the v0.2.49/v0.2.50 updater boundary and existing install channels.

Full review

No findings; docs-only; no local checks apply.

[github-actions]

Auto-approved: coreplane-switchboard[bot] reviewed this PR and posted an LGTM verdict (see its review). A repo admin enabled this via the auto-approve workflow.