New Lesson on Lazy

[jakubsvec001]

Hello,

I created a lesson on the Lazy module that I'd like to propose for the language tutorials section of ocaml.org.

You can find the draft on HackMD

Please suggest anything you would like, I'm happy to make several rounds of improvement.

Lesson implementation decisions:

This lesson is focused on beginners.

The first draft of this lesson is 345 lines, which is on the shorter side compared to
other lessons.

The surface area of the Lazy module is small, so I took the opportunity to
supplement the lesson with a thorough explanation of evaluation strategies. This is
supplemental, however, and can be shortened or removed based on your preferences.

Without the supplemental section, the lesson is only 200 lines long.