ci: add github Actions workflow

.github/workflows/build.yaml

@@ -0,0 +1,27 @@
+name: CI
+
+on:
+  push:
+    branches: [main, feature/tokamak]
+  pull_request:
+    branches: [main]
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        platform: [ubuntu-latest, macos-latest, windows-latest]
+    runs-on: ${{ matrix.platform }}
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Zig
+        uses: goto-bus-stop/setup-zig@v1
+        with:
+          version: master
+
+      - name: Build
+        run: |
+          zig build