[intro_supply_demand] Improvement suggestions

[HumphreyYang]

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This PR collects feedback from the reading group on intro_supply_demand.

Code

• [ ] Remove classes and use NamedTuple
• [ ] Add more explanation and comments on functions we used in the exercise scipy.optimize.minimize_scalar and scipy.optimize.newton

Content

• [x] Explain willingness to pay and the actual price. We can add a visualization showing consumers' willingness to pay and calculate the discrepancy to the actual price (Can we run a simulation?).

[jstac]

Thanks @HumphreyYang, nice summary.

We can add a visualization showing consumers' willingness to pay and calculate the discrepancy to the actual price

Perhaps we could do this with a discrete bar graph first, so that readers can understand the integral is just an approximation of a sum.

Also, could have an introductory discussion of integration as computing area under a curve, and provide the simple integration rules that we are going to use.