Add docs on "how to reproduce a 4.0 fit"

Created by: Zaharid

If we are going to make big claims about being reproducible, we should have a page on how to reproduce 4.0 fits, and fits in general. It doesn't have to be very complicated: Take this [link] runcard, this conda environment and [link] run a fit with them.

Expanding bit on where to find other fit runcards.