Add explanatory illustrations for pipeline to readme

At the moment our readme is quite dull with tools explained in plain text. We need to add illustrations to visually explain the pipeline to users on first sight. Here are some scribbles:

![](https://user-images.githubusercontent.com/527241/41095460-c5101e48-6a51-11e8-8388-00d1cc1a1454.png)

![](https://user-images.githubusercontent.com/527241/41095465-c7c423be-6a51-11e8-94d9-a3fd3a3c76f7.png)