📝 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"

cspell.json

@@ -45,7 +45,8 @@
         "todotasks",
         "connor",
         "injective",
-        "injectivity"
+        "injectivity",
+        "userland"
     ],
     "ignorePaths": ["dist", "node_modules", "coverage", "*.svg", ".gitignore"]
 }