Add workflow

.github/workflows/ci.yaml

@@ -0,0 +1,26 @@
+name: Prettier Check
+
+on:
+  push:
+    branches:
+      - *
+  pull_request:
+
+jobs:
+  prettier:
+    runs-on: ubuntu-latest
+
+    steps:
+    - name: Check out code
+      uses: actions/checkout@v2
+
+    - name: Set up Node.js
+      uses: actions/setup-node@v2
+      with:
+        node-version: 14  # or another version if you prefer
+
+    - name: Install dependencies
+      run: npm ci
+
+    - name: Check formatting with Prettier
+      run: npx prettier --check src/