Add note about finalizers required for audio store clean-up

osu.Game/Rulesets/UI/DrawableRulesetDependencies.cs

@@ -63,6 +63,7 @@ public DrawableRulesetDependencies(Ruleset ruleset, IReadOnlyDependencyContainer
 
         ~DrawableRulesetDependencies()
         {
+            // required to potentially clean up sample store from audio hierarchy.
             Dispose(false);
         }
 

osu.Game/Skinning/Skin.cs

@@ -36,6 +36,7 @@ protected Skin(SkinInfo skin)
 
         ~Skin()
         {
+            // required to potentially clean up sample store from audio hierarchy.
             Dispose(false);
         }