add a basic github-ci file for linux, windows and macos

.github/workflows/main.yml

@@ -0,0 +1,16 @@
+name: Build
+
+on: [push, pull_request]
+
+jobs:
+  build:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{matrix.os}}
+    steps:
+      - uses: actions/checkout@main
+      - run: |
+          cd example
+          cmake -B build
+          cmake --build build