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-multi-ping.pl.md

@@ -0,0 +1,20 @@
+# x-multi-ping.pl
+
+Ping multiple hosts with IPv4/IPv6 support.
+
+## Usage
+
+```bash
+x-multi-ping.pl [--loop|--forever] [--sleep N] host1 host2 ...
+```
+
+`--loop` keeps pinging each host until interrupted. `--sleep` controls
+the delay between attempts.
+
+### Example
+
+```bash
+x-multi-ping.pl --loop --sleep 2 example.com 1.1.1.1
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->