Create dockerimage.yml

.github/workflows/dockerimage.yml

+name: Docker Image CI
+on: [push]
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@master
+    - name: Build the Docker image
+      run: |
+        docker login --username=${{ secrets.DOCKER_HUB_USER }} --password=${{ secrets.DOCKER_HUB_PWD }}
+        docker build -t b3log/solo:latest .
+        docker push b3log/solo