infra: added auto theme readme generator script

.github/workflows/generate-theme-doc.yml

@@ -0,0 +1,35 @@
+name: Generate Theme Readme
+
+on:
+  push:
+    branches:
+      - master
+    paths:
+      - "themes/index.js"
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v1
+      - name: setup node
+        uses: actions/setup-node@v1
+        with:
+          node-version: "12.x"
+
+      - name: npm install, generate readme
+        run: |
+          npm ci
+          npm run theme-readme-gen
+        env:
+          CI: true
+
+      - name: Run Script
+        uses: skx/github-action-tester@master
+        with:
+          script: ./push-theme-readme.sh
+        env:
+          CI: true
+          PERSONAL_TOKEN: ${{ secrets.PERSONAL_TOKEN }}
+          GH_REPO: ${{ secrets.GH_REPO }}