Add documentation site

VitePress-based docs at website/ with landing page, guides, concept
explainers, real-world examples, and reference pages. Deployed to
GitHub Pages via Actions workflow.

Slims down README to point to the docs site.

Made-with: Cursor

Author: Topi Santakivi

.github/workflows/docs.yml

@@ -0,0 +1,53 @@
+name: Deploy docs
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - 'website/**'
+      - '.github/workflows/docs.yml'
+  workflow_dispatch:
+
+permissions:
+  contents: read
+  pages: write
+  id-token: write
+
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+          cache-dependency-path: website/package-lock.json
+
+      - name: Install dependencies
+        run: npm ci
+        working-directory: website
+
+      - name: Build
+        run: npm run build
+        working-directory: website
+
+      - uses: actions/upload-pages-artifact@v3
+        with:
+          path: website/.vitepress/dist
+
+  deploy:
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
+    needs: build
+    runs-on: ubuntu-latest
+    steps:
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4