feat: add bats tests, docs (#139)

* fix(test): ensure bats file list uses xargs

* docs(readme): use yarn for testing instructions

* fix(test): ensure pipelines fail properly

* docs(alias): fix table header

---------

Signed-off-by: Ismo Vuorinen <ismo@ivuorinen.net>

local/bin/php-switcher.md

@@ -0,0 +1,23 @@
+# php-switcher
+
+Switch between Homebrew-installed PHP versions or list installed versions.
+
+## Usage
+
+```bash
+php-switcher <version>|--auto [options]
+```
+
+Options:
+
+- `--installed` – list versions installed via Homebrew
+- `--current` – print currently active PHP version
+- `--auto` – read version from `.php-version` in current directory
+
+### Example
+
+```bash
+php-switcher 8.3
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->