Add customization example in docs notebook

[Beauprel]

Added a section describing how to customize plots, through arguments and through the ax object. Amongst other things, it demonstrates how to change a left-aligned title using the loc argument.

[sarahclaude]

Looks good!
I would change
2. By creating an object and using the Matplotlib methods on it..
by
2. Creating a Matplotlib axes class and applying its methods...

The section could also be put at the end of time series just before the maps.