📝 Add an alternatives section

Add a short README section under Alternatives, one heading per
alternative (ts-pattern, Effect.Match, match-iz and plain switch), each
saying what it is and what tiny-pattern-ts is or does differently. State
the data-last, pipe-friendly shape in Description.

- measure the footprint: ~0.2 kB minified + gzipped, not the
  unminified ~1.8 kB; ts-pattern is ~2 kB
- correct match-iz: it ships types, it just cannot prove exhaustiveness
- drop switchcase / ts-match (unmaintained)
- check off the backlog task

Resolves: backlog "Add comparison section vs. other TS pattern-matching libs"

backlog.tasks

@@ -27,9 +27,9 @@ Documentation:
     → previous section order: title, tagline, Synopsis, Description, Requirements, Examples, API, License, Contributing
     → previous Examples order: literal/exhaustive, typeof, structural/discriminated unions, when, any
 ☐ Create `examples/` directory with runnable snippets
-☐ Add comparison section vs. other TS pattern-matching libs in Readme.md
-    ☐ Why do we do this? => exhaustiveness encoded type safe
-    ☐ Why this form? little syntax, data last, very small, autocomplete, strict typing in the handler; for more features use ts-pattern
+✔ Add comparison section vs. other TS pattern-matching libs in Readme.md @done
+    ✔ Why do we do this? => exhaustiveness encoded type safe @done
+    ✔ Why this form? little syntax, data last, very small, autocomplete, strict typing in the handler; for more features use ts-pattern @done
 ✔ Write migration guide for users coming from discriminated unions @done (9/24/2026, 10:21:17 PM)
 ✔ Create backlog tasks for implementation @done (9/24/2026, 10:21:16 PM)
 ✔ Validate code fences in Markdown (start with README.md) — compile the TypeScript examples against `src/` so the docs cannot drift from the API @done