Update basic usage example

[gisellerosetta]

The examples can be more tutorialised by chunking them up into steps, each with light commentary and a code chunk, and then the combined code in a collapsible chunk at the end with a picture of the before and after. As a suggestion, the 1st most basic example might take the form:

• Import packages and process data, <code chunk 1>
• Define elements in the gptable with light explanation, <code chunk 2>
• Show alternative kwargs definition, <code chunk 3>
• Define the sheets, <code chunk 4>
• Write out the notebook (without __name__ == "__main__"), <code chunk 5>
• Picture of before and after, which is stored in the static directory.
• Text indicating the contents of the collapsible tab, followed by the tab containing code chunks 1-5 combined (perhaps with the kwargs part commented out?).

Definition of done:

• The section has a title describing it as a basic example.
• The code is chunked up in a clear way to break up the code.