Add example site and workflows

.github/workflows/deploy-example.yml

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+name: Deploy example site
+on:
+  push:
+    branches:
+      - main
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Deploy
+        uses: JamesIves/github-pages-deploy-action@v4
+        with:
+          branch: gh-pages
+          folder: test

.github/workflows/preview-example.yml

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+name: Preview example site
+on:
+  pull_request:
+    types:
+      - opened
+      - reopened
+      - synchronize
+      - closed
+concurrency: preview-${{ github.ref }}
+jobs:
+  deploy-preview:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Deploy preview
+        uses: rossjrw/pr-preview-action@v0
+        with:
+          source-dir: test

test/index.html

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+<p>Hello, world!</p>
+<p>This is a demonstration of the PR Preview action.</p>
+<p><a href="https://github.com/rossjrw/pr-preview-action">Learn more</a></p>