docs(location-timezone): add Compared to alternatives section

[ob-aion]

Summary

• Adds a ## Compared to alternatives section to the README, mirroring the pattern in @coroboros/clone.
• Compares @coroboros/location-timezone against i18n-iso-countries, countries-list, geo-tz (different input model — lat/lng polygon, not city name), and city-timezones (closest peer in shape).
• Table rows are feature-presence only (UN + CIA country forms, ISO 3166 codes, capital coords/tz, US state codes, city coords, city-name → tz lookup, cross-references, deps) — no raw performance numbers, since the alternatives don't share a methodology.
• Positioning paragraph names the differentiator (consolidation of five domains with cross-references resolved at parse time, behind O(1) Map/Set indexes).
• TOC entry added between Limitations and Contributing.

Test plan

• Render the README on github.com — anchor #compared-to-alternatives resolves from the TOC.
• Table renders with right-aligned status columns in GitHub-flavored markdown.
• No regressions in existing sections (Data, API, Subpath exports, Limitations).