Improve numpy foundations content

[jukent]

Numpy was specified by ClimateMatch as a chapter with areas for improvement.

“However, during our review, we identified some key information gaps, such as the absence of matrix multiplication in the NumPy Basics tutorial. Additionally, we noticed instances of verbose text that might be overwhelming for beginners.”

I am going to find out more about where we are verbose, but let's try to add matrix multiplication.