add CI

.github/workflows/ci.yml

@@ -0,0 +1,23 @@
+name: CI
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+    steps:
+      - name: Checkout
+        uses: actions/checkout
+      - name: Install node
+        uses: actions/setup-node
+      - name: Install npm dependencies
+        run: npm ci
+      - name: Compile typescript
+        run: npm run build
+      - name: Check for diffs
+        run: git diff --no-ext-diff --exit-code