Add some info on why 1-4 interactions are reduced.

Author: davidlmobley

paper/basic_training.tex

@@ -437,6 +437,7 @@ \subsubsection{Key concepts}
 These interactions are often present but reduced, though the exact amount of reduction differs by the energy function or force field family.
 For example, the AMBER family force fields usually reduce 1-4 electrostatics to $\frac{1}{1.2}$ of their original value, and 1-4 Lennard-Jones interactions to $\frac{1}{2}$ of their original value.
 1-4 interactions are essentially considered the borderline between the bonded and non-bonded regions.
+Because these are short-range interactions, they are potentially quite strong and there is potentially a risk of them overwhelming longer-range interactions, hence their typical reduction.
 
 
 %\end{itemize}