ci: add gh actions

.github/workflows/main.yml

@@ -0,0 +1,22 @@
+name: main
+
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  test:
+    name: Build
+    if: "!contains(github.event.commits[0].message, 'ci skip')"
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+    runs-on: ${{matrix.os}}
+    steps:
+      - uses: actions/checkout@v2
+      - uses: goto-bus-stop/setup-zig@v2
+        with:
+          version: 0.13.0
+      - run: zig build test