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-localip.md

@@ -0,0 +1,25 @@
+# x-localip
+
+Display local IPv4 and IPv6 addresses with optional interface filtering.
+
+## Usage
+
+```bash
+x-localip [--ipv4] [--ipv6] [interface]
+```
+
+- `--ipv4` – show only IPv4 addresses
+- `--ipv6` – show only IPv6 addresses
+- `interface` – limit output to the named interface
+
+## Example
+
+```bash
+# Show all addresses
+x-localip
+
+# IPv4 for wlan0
+x-localip --ipv4 wlan0
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->