Add wrap-up video of model families

Adding an overview of model families was proposed [here in the forum](https://mooc-forums.inria.fr/moocsl/t/end-of-course-comment/4748).

> I understand it is difficult to have focus on all type of modelling methods. Nevertheless I feel that as introduction could be useful to give [an] overview of all model families and their main focus points (for example SVM models, when to use, for what purpose, advantages & drawbacks…

I feel the most suitable way to do this is as a wrap-up video at the end of the course, giving a sensation of summary and closure.

Start with the issue and the linked forum proposal to define the intended model-family coverage and the wrap-up video's role in the course. Done means producing and integrating a summary video that explains the families, use cases, advantages, and drawbacks; no source file or test is named.

Written by the indexing model from the issue text.