IDEA: add more Julia code in the lecture notes

[bertdv]

(this is for the 2023/2024 edition).

I have received some feedback from past students that they find the transition to Julia difficult as it comes on top of conceptually difficult new lecture notes. I like to work on learning-about-Julia gradually through the lecture notes by adding small Julia examples of new lecture materials, and pointing out how the code differs from Python.

For instance, when we introduce the product rule, let's do a simple product rule example in Julia and point out some peculiarities of the Julia code. This way, the student gets a better understanding of the materials and at the same time learns how to code in Julia on the side.

feel free to comment.