Chore: create preview.yml (#21457)

.github/workflows/preview.yml

+name: Website Preview
+
+on: pull_request
+
+jobs:
+  preview:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      
+      - uses: actions/setup-node@v2
+        with:
+          node-version: '10.15.0'
+          registry-url: https://registry.npmjs.com/
+          
+      - uses: afc163/surge-preview@v1
+        id: preview_step
+        with:
+          surge_token: ${{ secrets.SURGE_TOKEN }}
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          dist: examples/element-ui/
+          build: |
+            npm run bootstrap
+            npm run deploy:build
+            
+      - name: Get the preview_url
+        run: echo "url => ${{ steps.preview_step.outputs.preview_url }}"