clarify where xp comes from

rules.tex

@@ -199,7 +199,7 @@ The suggested starting \glspl{xp} is 50, with up to 150 \glspl{xp} for more adva
 
 \subsection{Gaining \gls{xp}}
 
-Players receive \gls{xp} from the \gls{gm} for killing monsters, pious endeavours or fulfilling one's personal goals.
+Players receive \gls{xp} from the \gls{gm} for killing monsters, fulfilling their codes, and completing missions.
 Larger and more dangerous monsters garner more \gls{xp}, as do grander missions.
 \iftoggle{verbose}{%
 The personal goals and piety of a character are denoted by different codes of belief and gods.