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-foreach.md

@@ -0,0 +1,20 @@
+# x-foreach
+
+Run a command in each directory produced by another command.
+
+## Usage
+
+```bash
+x-foreach "<list-cmd>" "<cmd>"
+```
+
+- `list-cmd` – command that outputs directories
+- `cmd` – command to run inside each directory
+
+## Example
+
+```bash
+x-foreach "ls -d */" "git status"
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->