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/x-quota-usage.php.md

@@ -0,0 +1,14 @@
+# x-quota-usage.php
+
+Display filesystem quota usage in a human readable table.
+
+## Usage
+
+```bash
+x-quota-usage.php
+```
+
+Runs the `quota` command and formats the output. Requires PHP with the
+`shell_exec` function enabled.
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->