Add example demo page

https://vovanr.github.io/toggle-in-array

See: https://github.com/VovanR/hour-to-chinese-zodiac

Use `gh-pages` https://github.com/VovanR/parcel-demo/blob/master/package.json
```
  "deploy": "npm run build && gh-pages -d dist",
  "devDependencies": {
    "gh-pages": "^1.1.0",
  },
```