Update docs to be in line with existing code.

docs/modders/Map_Objects/Rewardable.md

@@ -515,7 +515,7 @@ canLearnSpells
 ```jsonc
 "creatures" : [
     {
-        "creature" : "archer",
+        "type" : "archer",
         "upgradeChance" : 30,
         "amount" : 20,
     }

lib/mapObjects/CRewardableObject.cpp

@@ -60,7 +60,7 @@ void CRewardableObject::grantAllRewardsWthMessage(const CGHeroInstance * context
 		
 	for (auto index : rewardIndices)
 	{
-		// TODO: Allow a single message for multiple / all rewards?
+		// TODO: Merge all rewards of same type, with single message?
 		grantRewardWithMessage(contextHero, index, false);
 	}
 	// Mark visited only after all rewards were processed