ard_1_intro_and_best_practices.ipynb make plots more readable

[emma-steuer]

The plots in this notebook are difficult to read and unorganized. They need to be reworked including:

1. Making them both the same size
2. Making the colourbar the same scale (i.e., making them both go from the same min and max, maybe each -1.0 to +1.0, to be consistent with how we define NDVI above?)
3. Setting NDVI as the colourbar title and having a more meaningful plot title. What are you showing? Yes, it's the NDVI, but of what?