Add a function that prettifies image plotting

Write a function in helpers.py that:

- uses the matplotlib.pyplot.imshow() function
- uses pyplot options to make the plot prettier in some way
- Any of the following could make the plot prettier, you can choose some or do all
- Add a title
- Add x and y labels
- Choose a custom color palette (Kudos if it's colorblind compliant)
- Display the x and y axes in lat / lon instead of pixels (requires a bit of math)

Add an example in `jupyter_notebooks/` (you can edit `tutorial.ipynb` or make your own notebook) which shows how to call this function and the cool options you added.