feat: documentation website using Vitepress

Adds documentation website using https://vitepress.dev.

Some decisions are questionable, for example creation of a symbolic link
for the README in the `docs/`. I wanted to preserve the ability to read
docs using Github. Maybe not needed.

Another issue, is the page outline for the `NixOS` chapter is too
narrow.

But should serve as a scaffold/basis for doing it properly.

.github/workflows/docs.yml

@@ -0,0 +1,47 @@
+name: Deploy VitePress site to Pages
+on:
+  push:
+    branches: ["main", "next", "next-nix-generate-docs"]
+  workflow_dispatch:
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+concurrency:
+  group: pages
+  cancel-in-progress: false
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 1
+      - uses: pnpm/action-setup@v3
+      - name: Setup Node
+        uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: pnpm
+      - name: Setup Pages
+        uses: actions/configure-pages@v4
+      - name: Install dependencies
+        run: pnpm install
+      - name: Build with VitePress
+        run: pnpm run docs:build
+      - name: Upload artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: docs/.vitepress/dist
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    needs: build
+    runs-on: ubuntu-latest
+    name: Deploy
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4