Add an introduction video link

Author: dadish

ScreenCast.md

@@ -16,10 +16,13 @@ Documentation for your api is easily accessible via GraphiQL interface.
 
 ![ProcessGraphQL Schema Documentation][img-documentation]
 
+[![ProcessGraphQL - Introduction][img-youtube-thumb]](https://www.youtube.com/watch?v=4M2VS5XAvts)
+
 Learn more from the [documentation](https://github.com/dadish/processgraphql#processgraphql).
 
 [img-query]: https://raw.githubusercontent.com/dadish/ProcessGraphQL/master/imgs/ProcessGraphQL-Query.gif
 [img-filtering]: https://raw.githubusercontent.com/dadish/ProcessGraphQL/master/imgs/ProcessGraphQL-Filtering.gif
 [img-fieldtypes]: https://raw.githubusercontent.com/dadish/ProcessGraphQL/master/imgs/ProcessGraphQL-Fieldtypes.gif
 [img-documentation]: https://raw.githubusercontent.com/dadish/ProcessGraphQL/master/imgs/ProcessGraphQL-Documentation.gif
+[img-youtube-thumb]: https://raw.githubusercontent.com/dadish/ProcessGraphQL/master/imgs/thumb.png
 [pw-selectors]: https://processwire.com/api/selectors/