Add map of neutronics interactions

[shimwell]

perhaps add a diagram like this to show where neutronics is useful
https://excalidraw.com/#json=A5FPlJNbxU4LVlMBVpdij,x8VZeUwpr-AmAE4cKbyHkg

[approx-infinity]

It's a great idea. It will help beginners identify areas that interest them and provide an initial sense of direction on what they can explore or work on next.