Update Docker builds to publish to ghcr.io & update README (#1067)

.github/workflows/pr-snapshot.yml

@@ -0,0 +1,86 @@
+name: Build snapshot of PR
+
+on: pull_request
+
+env:
+  REGISTRY_IMAGE: ghcr.io/museofficial/muse
+
+jobs:
+  build:
+    name: Build snapshot
+    strategy:
+      matrix:
+        runner-platform:
+          - ubuntu-latest
+          - namespace-profile-default-arm64
+        include:
+          - runner-platform: ubuntu-latest
+            build-arch: linux/amd64
+            tagged-platform: amd64
+          - runner-platform: namespace-profile-default-arm64
+            build-arch: linux/arm64
+            tagged-platform: arm64
+    runs-on: ${{ matrix.runner-platform }}
+    steps:
+      - name: Prepare
+        run: |
+          platform=${{ matrix.build-arch }}
+          echo "PLATFORM_PAIR=${platform//\//-}" >> $GITHUB_ENV
+
+      - name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ${{ env.REGISTRY_IMAGE }}
+          tags: type=ref,event=pr
+
+      - name: Set up Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Get current time
+        uses: josStorer/get-current-time@v2
+        id: current-time
+
+      - name: Build
+        id: build
+        uses: docker/build-push-action@v6
+        with:
+          outputs: type=docker,dest=/tmp/image.tar
+          tags: ${{ steps.meta.outputs.tags }}
+          platforms: ${{ matrix.build-arch }}
+          build-args: |
+            COMMIT_HASH=${{ github.sha }}
+            BUILD_DATE=${{ steps.current-time.outputs.time }}
+
+      - name: Export digest
+        run: |
+          mkdir -p /tmp/digests
+          digest="${{ steps.build.outputs.digest }}"
+          touch "/tmp/digests/${digest#sha256:}"
+
+      - name: Upload image
+        uses: actions/upload-artifact@v4
+        with:
+          name: image-${{ env.PLATFORM_PAIR }}
+          path: /tmp/image.tar
+          if-no-files-found: error
+          retention-days: 1
+
+      - name: Save PR number in artifact
+        shell: bash
+        env:
+          PR_NUMBER: ${{ github.event.number }}
+        run: echo $PR_NUMBER > /tmp/pull_request_number.txt
+      - name: Upload PR number
+        uses: actions/upload-artifact@v4
+        with:
+          name: pull_request_number
+          path: /tmp/pull_request_number.txt
+          overwrite: true