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-up.md

@@ -0,0 +1,19 @@
+# x-when-up
+
+Wait for a host to respond to ping before running a command.
+
+## Usage
+
+```bash
+x-when-up <host> <command...>
+```
+
+If the command is `ssh`, the host argument may be omitted.
+
+## Example
+
+```bash
+x-when-up 1.2.3.4 ssh 1.2.3.4
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->