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-validate-sha256sum.sh.md

@@ -0,0 +1,14 @@
+# x-validate-sha256sum.sh
+
+This script contains a helper for sha256 validating your downloads
+
+## Usage
+
+```bash
+x-validate-sha256sum.sh file sha256sum
+```
+
+The script computes the SHA256 hash of `file` and compares it to the
+expected value. It exits non-zero if the sums differ.
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->