[Quality] Add CI for formatting (#343)

.github/workflows/yapf.yml

@@ -0,0 +1,31 @@
+name: yapf
+
+on:
+  # Trigger the workflow on push or pull request,
+  # but only for the main branch
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+jobs:
+  yapf:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python-version: ["3.10"]
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v2
+      with:
+        python-version: ${{ matrix.python-version }}
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install yapf==0.32.0
+        pip install toml==0.10.2
+    - name: Running yapf
+      run: |
+        yapf --diff --recursive vllm --exclude 'vllm/model_executor/parallel_utils/**'