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/dfm.md

@@ -0,0 +1,26 @@
+# dfm
+
+Dotfiles manager and installation helper. Provides wrappers for many
+setup tasks defined in this repository.
+
+## Usage
+
+```bash
+dfm <command> [options]
+```
+
+Common commands include:
+
+- `install` – install tools or run platform specific setup
+- `brew` – manage Homebrew packages
+- `docs` – regenerate markdown documentation
+
+Set `VERBOSE=1` to see debug output.
+
+### Example
+
+```bash
+dfm install all
+```
+
+<!-- vim: set ft=markdown spell spelllang=en_us cc=80 : -->