Add more info to Physics Guides

[tvami]

I'd like to have the coordinate system definitions under the Physics Guides in our text, especially since tracking uses the coordinates in a different order.

Also I think having a rough geometrical description of the detector, i.e the Z of the tagger, recoil, ECAL, HCAL; then max X/Y of each of these.

These are questions that come up very often, and sometimes the white paper use useful, sometimes it's not, and then going to the GDML is not that fun