Added GitHub workflow for CI

.github/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: 'CI'
+
+on:
+  push:
+    tags: ['*']
+    branches: ['*']
+  pull_request:
+    branches: ['*']
+  workflow_dispatch:
+
+jobs:
+
+  build:
+    name: 'Build ${{ matrix.arch }} image'
+    runs-on: 'ubuntu-latest'
+    strategy:
+      matrix:
+        arch: ['amd64', 'arm64v8', 'arm32v7']
+    steps:
+      - name: 'Checkout project'
+        uses: 'actions/checkout@v1'
+      - name: 'Build image'
+        run: |
+          make binfmt-register
+          make IMAGE_BUILD_OPTS="--pull" "build-${{ matrix.arch }}-image"