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/git-attributes.md

@@ -0,0 +1,25 @@
+# git-attributes
+
+Checks that every tracked file has a matching pattern in `.gitattributes`.
+Can optionally suggest or write missing rules.
+
+## Usage
+
+```bash
+git-attributes [options]
+```
+
+Options include:
+
+- `-v, --verbose` – show progress information
+- `-e, --exit` – exit with non-zero status if missing rules
+- `-p, --pattern <glob>` – pattern to check (default: `text: auto`)
+- `-w, --write` – append suggestions to `.gitattributes`
+
+### Example
+
+```bash
+git-attributes -v --write
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->