clarify berserker knack

knacks.tex

@@ -24,6 +24,8 @@ You enter a bloodthirsty rage when in battle.
 After the first round, you gain a +1 bonus to Speed.
 After the second round, you gain a +1 bonus to Strength.
 
+You lose the bonuses if you spend a round without attacking.
+
 \subsubsection{Brawler}
 
 The character receives +2 to Strike when making unarmed attacks or grappling.