vercel preview workflow

.github/workflows/preview.yml

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+name: Build and Deploy Preview environment on Vercel
+on:
+  pull_request:
+    branches: ['main']
+
+jobs:
+  deploy-job:
+    runs-on: ubuntu-latest
+
+    # Update the "Preview" environment with the Vercel deployed URL
+    environment:
+      name: Preview
+      url: ${{ steps.vercel-deploy.outputs.deployment_url }}
+
+    steps:
+      - uses: actions/setup-node@v4
+      - uses: actions/checkout@v4
+      - id: vercel-deploy
+        run: |
+          npx -y vercel deploy --target=preview --token=${{ secrets.VERCEL_TOKEN }} \
+            --build-env MDX=docs \
+            --build-env NEXT_PUBLIC_LIBNAME="Poimandres" \
+            --build-env NEXT_PUBLIC_LIBNAME_SHORT="pmndrs" \
+            --build-env BASE_PATH= \
+            --build-env DIST_DIR= \
+            --build-env OUTPUT=export \
+            --build-env HOME_REDIRECT=/introduction \
+            --build-env MDX_BASEURL="https://github.com/${{ github.repository }}/raw/${{ github.head_ref }}/docs" \
+            --build-env EDIT_BASEURL="https://github.com/${{ github.repository }}/edit/${{ github.head_ref }}/docs" \
+            --build-env NEXT_PUBLIC_URL="$VERCEL_PROJECT_PRODUCTION_URL" \
+            --build-env ICON="🖨️" \
+            --build-env LOGO= \
+            > deployment-url.txt
+
+          echo "deployment_url=$(cat deployment-url.txt)" >> $GITHUB_OUTPUT
+        env:
+          VERCEL_ORG_ID: ${{ secrets.VERCEL_ORG_ID }}
+          VERCEL_PROJECT_ID: ${{ secrets.VERCEL_PROJECT_ID }}

docs/introduction.mdx

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+---
+title: Poimandres documentation
+description: A documentation generator for `pmndrs/*` projects.
+---
+
+![](gutenberg.jpg)
+
+## Heading 1
+
+Lorem ipsum