Collaborative filtering example

How can collaborative filtering (with probabilistic matrix factorization) be implemented with FastAI.jl? Are there any snippets of this or plans to add it soon? I haven't seen examples of this even with Flux.jl so I'm a little bit lost, only MLP and Convnets. Also, I'm learning Julia and would love to contribute to this package, If there are some hints on how to do this, I'll gladly try to implement it and open a PR.

Start by reviewing the existing MLP and ConvNets examples in FastAI.jl and the available Flux.jl examples. Clarify whether the expected contribution is documentation, an example, or package support for probabilistic matrix factorization, and define completion before implementation.

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