Add CI workflow

.github/workflows/main.yml

@@ -0,0 +1,22 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@master
+
+      - name: Build
+        run: |
+          make -j$(nproc) -C tools
+          if ! git diff-index --quiet HEAD --; then
+            echo 'Uncommitted changes detected:'
+            git diff-index HEAD --
+            return 1
+          fi