Add mdbook to docs workflow (#4437)

Based on
https://github.com/rust-lang/mdBook/wiki/Automated-Deployment%3A-GitHub-Actions

.github/workflows/docs.yml

@@ -28,12 +28,22 @@ jobs:
     steps:
       - name: Checkout
         uses: actions/checkout@v4
+      - name: Install latest mdbook
+        run: |
+          tag=$(curl 'https://api.github.com/repos/rust-lang/mdbook/releases/latest' | jq -r '.tag_name')
+          url="https://github.com/rust-lang/mdbook/releases/download/${tag}/mdbook-${tag}-x86_64-unknown-linux-gnu.tar.gz"
+          mkdir mdbook
+          curl -sSL $url | tar -xz --directory=./mdbook
+          echo `pwd`/mdbook >> $GITHUB_PATH
+      - name: Build mdbook
+        run: |
+          mdbook build docs
       - name: Setup Pages
         uses: actions/configure-pages@v5
       - name: Upload artifact
         uses: actions/upload-pages-artifact@v3
         with:
-          path: "docs"
+          path: "docs/book"
       - name: Deploy to GitHub Pages
         id: deployment
         uses: actions/deploy-pages@v4