feat: add coding standard action (#51)

coding-standard/README.md

@@ -0,0 +1,30 @@
+# Magento 2 Coding Standard Action
+
+A Github Action that runs the Magento Coding Standard.
+
+## Inputs
+
+See the [action.yml](./action.yml)
+
+## Usage
+
+```yml
+name: Coding Standard
+
+on:
+  push:
+    branches:
+    - main
+  pull_request:
+    branches:
+    - main
+
+jobs:
+  coding-standard:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: graycoreio/github-actions-magento2/coding-standard@main
+      with:
+        version: 25 # Optional, will use the latest if omitted.
+        path: app/code # Optional, will be used when event is not a pull request.
+```