add docker login

.github/workflows/build.yaml

@@ -10,18 +10,29 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - name: checkout
+      -
+        name: checkout
         uses: actions/checkout@v2
-      - name: set up QEMU
+      -
+        name: set up QEMU
         uses: docker/setup-qemu-action@v1
-      - name: set up buildx
+      -
+        name: set up buildx
         id: buildx
         uses: docker/setup-buildx-action@v1
         with:
           buildkitd-flags: --debug
-      - name: platforms
+      -
+        name: platforms
         run: echo ${{ steps.buildx.outputs.platforms }}
-      - name: build
+      -
+        name: login to docker hub
+        uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: build
         run: cd contrib/docker && ./build.sh release
 #      - name: configure and build
 #        run: ./make_debian.sh