docs: add documentation

Author: tyrann0us

README.md

@@ -39,6 +39,7 @@ groups here:
 
 * Assets linting and formatting with [`@wordpress/scripts`](./docs/wp-scripts.md)
 * Linting, formatting, and testing tools for [PHP](./docs/php.md)
+* [Linting GitHub Actions workflow files](./docs/lint-workflows.md)
 * Unit tests for [JavaScript](./docs/js.md)
 * Assets compilation with [Composer Asset Compiler](./docs/assets-compilation.md) or
   the [Build and push](./docs/build-and-push-assets.md) approach

docs/lint-workflows.md

@@ -0,0 +1,15 @@
+# Lint GitHub Actions workflows
+
+This workflow runs [actionlint](https://github.com/rhysd/actionlint). It does so by executing the
+linter inside a Docker container using the official `actionlint` Docker image.
+
+**Example:**
+
+```yml
+name: Lint GitHub Actions workflows
+on:
+  pull_request:
+jobs:
+  lint-workflows:
+    uses: inpsyde/reusable-workflows/.github/workflows/lint-workflows.yml@main
+```