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-ip.md

@@ -0,0 +1,19 @@
+# x-ip
+
+Fetch your public IP address using `curl`.
+
+## Usage
+
+```bash
+x-ip [curl-options]
+```
+
+Any arguments are passed directly to `curl`.
+
+### Example
+
+```bash
+x-ip -4
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->