Add docker image

.github/workflows/docker.yml

@@ -0,0 +1,43 @@
+name: Build Docker Images
+on:
+  push:
+    tags:
+      - v*
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: "The tag version you want to build"
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Setup Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.repository_owner }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Docker metadata
+        id: metadata
+        uses: docker/metadata-action@v3
+        with:
+          images: ghcr.io/sagernet/sing-box
+      - name: Get tag to build
+        id: tag
+        run: |
+          if [[ -z "${{ github.event.inputs.tag }}" ]]; then
+            echo ::set-output name=tag::ghcr.io/sagernet/sing-box:${{ github.ref_name }}
+          else
+            echo ::set-output name=tag::ghcr.io/sagernet/sing-box:${{ github.event.inputs.tag }}
+          fi
+      - name: Build and release Docker images
+        uses: docker/build-push-action@v2
+        with:
+          platforms: linux/386,linux/amd64
+          target: dist
+          tags: ${{ steps.tag.outputs.tag }}
+          push: true