Prominently link to Michael Clarkson's video series on OCaml

[pmetzger]

Michael Clarkson, a lecturer at Cornell, has put his very high quality Introduction to OCaml videos up on Youtube. See
https://www.youtube.com/watch?v=MUcka_SvhLw&list=PLre5AT9JnKShBOPeuiD9b-I4XROIJhkIU
for the full playlist so far.

His associated textbook, "OCaml Programming: Correct + Efficient + Beautiful", is also now online at https://cs3110.github.io/textbook/cover.html

I think the videos should get prominent linkage on the site; they're probably the best in terms of production values I've seen so far. The textbook also should be linked to.