Improve GitHub Actions workflows

.github/workflows/ci.yml

@@ -45,3 +45,35 @@ jobs:
         working-directory: ${{env.SRC_DIR}}
         run: make all
 
+  Hadolint:
+    name: Hadolint
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Check dockerfiles with Hadolint
+        uses: essentialkaos/hadolint-action@v1
+        with:
+          files: Dockerfile
+
+  DockerBuild:
+    name: Docker Build Check
+    runs-on: ubuntu-latest
+
+    needs: Hadolint
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Login to DockerHub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build Docker image
+        run: |
+          docker build -f Dockerfile -t rsz .