Add a recommendation thingy

[namsnath]

Something like, since you chose this course, you might want to take this too. Or something like, Other people have taken B when they took A.

This is a major feature that would require leveraging the data in the DB and adding routes to provide the recommendations to the client.

There is no defined structure to this feature. Ideation and Suggestions on how to do this with Node and Mongo is welcomed.