Add GitHub Actions workflow for Docker image build

.github/workflows/main.yml

@@ -0,0 +1,29 @@
+name: Build and push Docker image
+
+on:
+  push:
+    branches: [ "main" ]
+
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Log in to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push image
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          push: true
+          tags: subgplayz/plugindownloader:latest