show talkable integration steps

1. add `<script src="//d2jjzw81hqbuqv.cloudfront.net/integration/clients/plastc.min.js"></script>` somewhere on your website

2. call the talkable code in src/js/app.js

3. in your css somewhere, you need to have this snippet:

```css
#talkable-container-pp iframe {
  z-index: 2000000002 !important;
}
```