chore: Add actions build

Author: kevee

.github/workflows/build.yml

@@ -0,0 +1,23 @@
+name: Build site
+on:
+  push:
+    branches:
+      - gatsby
+jobs:
+  deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Install
+        run: npm install
+
+      - name: Build
+        run: npm run build
+
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./public
+          cname: neaps.js.org