Add an overview of loss functions to the documentation
Created by: RoyStegeman
This addresses #1478 (closed).
This adds an overview of the loss functions we use in NNPDF to the documentation. The page itself does not go into much detail but I think it links to the relevant resources so it can be used as a reference in case someone is confused about the definition of the chi squared used in various places.
@Zaharid is this roughly what you had in mind?
Closes #1478 (closed)