Update README.md

[bguidolim]

Summary

Changes

Test plan

• swift test passes locally
• swiftformat --lint . and swiftlint pass without violations
• Affected commands verified with a real pack (e.g. mcs sync, mcs doctor)

Checklist for engine changes

Only check items that apply to this PR. Delete irrelevant ones.

• .shellCommand components have supplementaryDoctorChecks defined (deriveDoctorCheck() returns nil for shell actions)
• Any fix() implementation does cleanup/migration only — never installs or registers resources
• State migrations are guarded by isNeeded() to stay idempotent with mcs sync
• New file write/copy/delete paths use PathContainment.safePath() and handle the nil (escape) case
• Docs updated if behavior changed (CLAUDE.md, docs/, techpack.yaml schema in ExternalPackManifest.swift)