Add github workflow for PRs

.github/workflows/pull-request.yml

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+name: Pull Requests
+
+on:
+  pull_request:
+    branches: [ mainline ]
+
+  workflow_dispatch:
+
+# A workflow run is made up of one or more jobs that can run sequentially or in parallel
+jobs:
+  # This workflow contains a single job called "build"
+  build:
+    # The type of runner that the job will run on
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Cache node modules
+        uses: actions/cache@v2
+        env:
+          cache-name: cache-node-modules
+        with:
+          # npm cache files are stored in `~/.npm` on Linux/macOS
+          path: ~/.npm
+          key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-build-${{ env.cache-name }}-
+            ${{ runner.os }}-build-
+            ${{ runner.os }}-
+
+      # Runs a single command using the runners shell
+      - name: Setup Node.js environment
+        uses: actions/setup-node@v2
+        with:
+          node-version: '14'
+      - name: Install dependencies 📦
+        run: yarn install --frozen-lockfile
+      - name: Build 🛠
+        run: yarn build
+      - name: Deploy preview🔎
+        run: yarn deploy:preview | tee output.log
+        env:
+          NETLIFY_AUTH_TOKEN: ${{ secrets.NETLIFY_AUTH_TOKEN }}
+          NETLIFY_SITE_ID: ${{ secrets.NETLIFY_SITE_ID }}
+      - name: Extract draft url 📝
+        id: draft-url
+        run: |
+          URL=$(cat output.log | fgrep "Website Draft URL")
+          echo $URL
+          echo ::set-output name=url::$(echo $URL)
+        shell: bash
+      - uses: mshick/add-pr-comment@v1
+        with:
+          message: |
+            **Latest preview link**
+
+            Please check out the preview link to ensure that the doc site renders correctly
+            🌏 ${{ steps.draft-url.outputs.url }}!
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          repo-token-user-login: 'github-actions[bot]'
+          allow-repeats: false # This is the default
+

.github/workflows/template.md

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+Check out the draft URL: