Closes #20. Added some dependencies

[gpcureton]

Closes #20 . Added routine for multiplying integers, an plotting an image using Altair.

[lwasser]

hey there @gpcureton thank you for this PR! the one challenge here that we need to think through is we can't delete this add_numbers.py module. this is because we use it in our trainings as an example module that people make. And in our tutorials as well. it's a core simple module that people can quickly make without thinking much about the code within the function there.

So we want user to be able to access this add_numbers.py module.

I'd prefer to keep the add_numbers module as is. BUT we can then rename your simple_arithmetic module to be something more specific that includes numpy or another package.

Let me know what you think.