chore(CI): add gh-pages deploy workflow

Author: Pyrax

.github/workflows/github-pages.yml

@@ -0,0 +1,35 @@
+name: github pages
+
+on:
+  push:
+    branches:
+      - master
+
+jobs:
+  deploy:
+    runs-on: ubuntu-18.04
+    steps:
+      - uses: actions/checkout@v2
+
+      - name: Setup Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: '12.x'
+
+      - name: Cache dependencies
+        uses: actions/cache@v2
+        with:
+          path: ~/.yarn
+          key: ${{ runner.os }}-node-${{ hashFiles('**/yarn.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-node-
+
+      - run: yarn install --frozen-lockfile
+      - run: yarn test
+      - run: yarn predeploy:prefix  # builds the docs site with --prefix-paths for gh-pages
+
+      - name: Deploy
+        uses: peaceiris/actions-gh-pages@v3
+        with:
+          github_token: ${{ secrets.GITHUB_TOKEN }}
+          publish_dir: ./www/public