workflow: build caramel sd-image

testing if github likes this..

.github/workflows/cachix.yml

@@ -60,3 +60,29 @@ jobs:
           name: lava
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
       - run: nix build -L .#packages.aarch64-linux.nixUnstable
+
+  build-img:
+    runs-on: ubuntu-latest
+    name: Build caramel-img for aarch64-linux
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+      - uses: dbhi/qus/action@main
+        with:
+          targets: arm aarch64
+      - uses: cachix/install-nix-action@v17
+        with:
+          install_url: https://github.com/numtide/nix-unstable-installer/releases/download/nix-2.12.0pre20220930_89ca75c/install
+          extra_nix_config: |
+            extra-platforms = aarch64-linux arm-linux
+            experimental-features = nix-command flakes
+      - uses: cachix/cachix-action@v10
+        with:
+          name: lava
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - run: nix build -L .#packages.aarch64-linux.caramel-img
+      - uses: actions/upload-artifact@v3
+        with:
+          name: caramel-sdimage
+          path: result/sd-image/*