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-compare-versions.py.md

@@ -0,0 +1,14 @@
+# x-compare-versions.py
+
+Compare version strings using Python's packaging library.
+
+## Usage
+
+```bash
+echo "1.2.3 >= 1.0.0" | x-compare-versions.py
+```
+
+The script reads comparison expressions from standard input and exits
+with status 0 if all comparisons are true.
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->