Add workflow for publishing image

Signed-off-by: Craig Jellick <[email protected]>

.github/workflows/publish.yaml

@@ -0,0 +1,27 @@
+name: Publish acorn image
+
+on:
+  push:
+    tags:
+      - "v*"
+
+jobs:
+  publish:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - uses: acorn-io/actions-setup@v2
+        with:
+          acorn-version: "main"
+      - uses: acorn-io/actions-login@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Set tag
+        run: echo "TAG=${GITHUB_REF#refs/*/}" >> $GITHUB_ENV
+      - name: Build and Publish
+        run: |
+          acorn build --platform linux/amd64 --platform linux/arm64 --push -t ghcr.io/acorn-io/hello-world:${TAG} .
+          acorn copy ghcr.io/acorn-io/hello-world:${TAG} ghcr.io/acorn-io/hello-world:latest