Add a quick notebook for current implementation

[brandynlucca]

Add a quick notebook that walks through the current methods through #222 alongside the upcoming kriging code refactoring/debugging update.

[brandynlucca]

A Jupyter notebook providing an example workflow of echopop has been added to /docs and is available/rendered when viewing the ReadTheDocs documentation page (Example workflows and analyses).

This can therefore be closed once PR #241 is merged.