ci: set up GHA

The workflow definition is modeled after that of
loongson-community/areweloongyet.

.github/workflows/deploy.yml

@@ -0,0 +1,58 @@
+name: Deploy to GitHub Pages
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  build_and_upload:
+    name: Build pages and upload
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout the repo
+        uses: actions/checkout@v4
+      - name: Set up mdBook
+        uses: peaceiris/actions-mdbook@v2
+        with:
+          mdbook-version: '0.4.40'
+      - name: Build website
+        run: mdbook build
+
+      - name: Upload pages artifacts (Main branch)
+        if: ${{ github.ref == 'refs/heads/main' }}
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: './book/'
+          name: 'gh-pages-${{github.sha}}'
+
+      - name: Upload pages artifacts (PR)
+        if: ${{ github.ref != 'refs/heads/main' }}
+        uses: actions/upload-artifact@v4
+        with:
+          path: './book/'
+          name: 'pages-${{github.sha}}'
+
+  deploy:
+    if: ${{ github.ref == 'refs/heads/main' }}
+    concurrency:
+      group: "pages"
+      cancel-in-progress: true
+    runs-on: ubuntu-latest
+    needs: build_and_upload
+    permissions:
+      contents: read
+      pages: write
+      id-token: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deploy.outputs.page_url }}
+    steps:
+      - name: Setup Pages
+        uses: actions/configure-pages@v5
+      - name: Deploy to GitHub Pages
+        id: deploy
+        uses: actions/deploy-pages@v4
+        with:
+          artifact_name: 'gh-pages-${{github.sha}}'