add GitHub workflow

.github/workflows/docker-image.yml

@@ -0,0 +1,29 @@
+name: Docker Image CI
+
+on:
+  push:
+    branches: ["master"]
+  pull_request:
+    branches: ["master"]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Build the Docker image
+        run: docker build . --file Dockerfile --tag weihua:latest
+
+      - name:
+          Install ssh keys
+          # check this thread to understand why its needed:
+          # <https://stackoverflow.com/a/70447517>
+        run: |
+          install -m 600 -D /dev/null ~/.ssh/id_rsa
+          echo "${{ secrets.M }}" > ~/.ssh/id_rsa
+          ssh-keyscan -H junction.nyman.dev > ~/.ssh/known_hosts
+
+      - name: Copy image to server
+        run: docker save weihua:latest | bzip2 | ssh [email protected] "docker load && cd backend && docker compose up -d"