feat: add prettier workflow

.github/workflows/prettier.yml

@@ -0,0 +1,25 @@
+name: Prettier
+
+on:
+  pull_request:
+  push:
+    branches:
+    - master
+
+jobs:
+  prettier:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Checkout
+      uses: actions/checkout@v2
+      with:
+        ref: ${{ github.head_ref }}
+
+    - name: Prettify code
+      uses: creyD/prettier_action@v3.0
+      with:
+        prettier_options: --write **/*.{html,js,md}
+        commit_message: 'docs: prettify code'
+      env:
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}