Add a bit of documentation

src/game/combat.ts

@@ -244,6 +244,9 @@ export class UniformRandomDamageFormula implements DamageFormula {
   }
 }
 
+/**
+ * A [[DamageFormula]] that uses the attacker's stats
+ */
 export class StatDamageFormula implements DamageFormula {
   constructor (private factors: Array<{ stat: Stat|VoreStat; fraction: number; type: DamageType; target: Vigor|Stat }>) {
 
@@ -592,6 +595,7 @@ export class Effective {
     return []
   }
 }
+
 /**
  * A displayable status effect
  */

src/game/combat/perks.ts

@@ -7,6 +7,9 @@ import { DamageConsequence, LogConsequence } from './consequences'
 import { LogLine } from '../interface'
 import * as Words from '../words'
 
+/**
+ * A Perk is like a permanent status effect for a creature.
+ */
 export abstract class Perk extends Effective {
   constructor (public name: TextLike, public desc: TextLike) {
     super()