Add document workflow.

.github/workflows/docs.yml

@@ -0,0 +1,41 @@
+name: docs
+
+on:
+  push:
+    branches: [main, docs]
+    paths:
+      - 'docs/**'
+      - '.github/workflows/docs.yml'
+  workflow_dispatch:
+
+jobs:
+  docs:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 0
+
+      - name: Setup pnpm
+        uses: pnpm/action-setup@v2
+        with:
+          version: 7
+          run_install: true
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v3
+        with:
+          node-version: 18
+          cache: pnpm
+
+      - name: Build VuePress site
+        run: pnpm docs:build
+
+      - name: Deploy to GitHub Pages
+        uses: crazy-max/ghaction-github-pages@v2
+        with:
+          target_branch: gh-pages
+          build_dir: docs/.vuepress/dist
+        env:
+          GITHUB_TOKEN: ${{ secrets.ACTION_TOKEN }}