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-when-down.md

@@ -0,0 +1,17 @@
+# x-when-down
+
+Wait until a host stops responding to ping, then run a command.
+
+## Usage
+
+```bash
+x-when-down <host> <command...>
+```
+
+## Example
+
+```bash
+x-when-down 1.2.3.4 echo "server down"
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->