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-sha256sum-matcher.md

@@ -0,0 +1,22 @@
+# x-sha256sum-matcher
+
+Compare two files by calculating their SHA256 checksums.
+
+## Usage
+
+```bash
+x-sha256sum-matcher [options] file1 file2
+```
+
+Options:
+
+- `-v` – verbose output
+- `-h, --help` – show help
+
+### Example
+
+```bash
+x-sha256sum-matcher original.iso download.iso
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->