added a comment about FAQ regarding mfact meaning

config.def.h

@@ -24,7 +24,7 @@ static Rule rules[] = {
 };
 
 /* layout(s) */
-static float mfact      = 0.55;
+static float mfact      = 0.55; /* factor of master area size [0.05..0.95] */
 static Bool resizehints = True; /* False means respect size hints in tiled resizals */
 
 static Layout layouts[] = {