Add an empirical lecture on commodity supply dynamics

[jstac]

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As suggested by Serge. Use data on cotton exports from Benin?

This could be a lecture on how to estimate a Markov chain using ML, with cotton output/exports as the state. We have code for this in quantecon.py.

And/or estimate as an AR process.

Presumably there will be seasonal fluctuations, so this will have to be part of the state.

[jstac]

@HengchengZhang Could you please start researching this?

We will be teaching this material to African students so it would be good to collect data on commodity harvests from African countries. Perhaps you could begin by making a list of data sources? What frequency are they and how far back do they go?

Once we have this information, let's discuss how we should estimate. @HumphreyYang might be interested in collaborating with you on this project.