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-backup-folder.md

@@ -0,0 +1,20 @@
+# x-backup-folder
+
+Create a compressed archive of a folder with a timestamped name.
+
+## Usage
+
+```bash
+x-backup-folder <folder> [archive-name]
+```
+
+- `folder` – directory to back up
+- `archive-name` – optional prefix for the generated tar.gz
+
+## Example
+
+```bash
+x-backup-folder ~/Documents Notes
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->