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-ssl-expiry-date.md

@@ -0,0 +1,22 @@
+# x-ssl-expiry-date
+
+Check the expiry date of an SSL certificate for one or more hosts.
+
+## Usage
+
+```bash
+x-ssl-expiry-date [-d] [-p PORT] host1 host2 ...
+```
+
+Options:
+
+- `-d` – show days left instead of the full date
+- `-p <port>` – use custom port (default: 443)
+
+### Example
+
+```bash
+x-ssl-expiry-date -d github.com
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->