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>

tests/dfm.bats

@@ -0,0 +1,11 @@
+#!/usr/bin/env bats
+
+setup() {
+  export DOTFILES="$PWD"
+}
+
+@test "dfm help shows usage" {
+  run bash local/bin/dfm help
+  [ "$status" -eq 0 ]
+  [[ "$output" == *"Usage: dfm"* ]]
+}