add workflow

.github/workflows/build.yml

@@ -0,0 +1,22 @@
+name: build
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [ master ]
+  schedule:
+    # Build the image regularly (each Friday)
+    - cron: '23 04 * * 5'
+
+jobs:
+  build:
+    name: Build
+    runs-on: "ubuntu-20.04"
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Build an image from Dockerfile
+        run: |
+          make
+