add custom docker builder, part of #81

.github/workflows/release.yaml

@@ -15,6 +15,8 @@ jobs:
     - name: Get tag
       id: vars
       run: echo ::set-output name=tag::${GITHUB_REF#refs/*/}
+    - name: Create a new container builder
+      run: docker buildx create --name builder && docker buildx use builder
     - name: Build the container image
       run: docker buildx build --platform linux/arm/v7,linux/arm64/v8,linux/amd64 --tag $IMAGE_NAME .
     - name: Log into GitHub Container Registry