Add Docker buildx stage

Author: adamtheturtle

.github/workflows/ci.yml

@@ -22,6 +22,9 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+
       - name: Build base Docker image
         uses: docker/build-push-action@v2.7.0
         with: