WIP: Tutorial on shot noise and photon arrival times

@bernardo.arus @asli.ergin Can you two take a look at the first section of this tutorial and provide feedback? The goal is to provide and introduction to shot noise and how it relates to our experiments.

@jian.cui @korneel.ridderbeek Can you provide feedback on the section section of this tutorial? It turned into a short introduction to photon correlation, which might be worthwhile to expand for your work.