Knife-edge scan and Fluence calculation example

We need to add in the RTD documentation a clear notebook showing an example of spot size and fluence calculation.

There is already something in #48

We should consider copying some of the data to SCS XMPL proposal @carinanc

assigned to @mercadil

mentioned in merge request !276 (merged)

closed with merge request !276 (merged)

mentioned in commit bc2d8b11