Implementation of a simple analytical example for the user guide

I implemented the simple analytical example for the user guide.

The matching user guide text written with this example can be found here: https://docs.google.com/document/d/104LJjg5tJayqVLODrcAz5LNjRTUcMzkF8ckMAXe5lgE/edit

On the model explanation, we could add a bit of text, other than that I would say it's pretty much done. Please let me know if you have any change requests.