docs(website): more notes on addMutationListener

Author: christianalfoni

packages/overmind-website/api/overmind.md

@@ -10,7 +10,7 @@ You can pass a second argument to the **Overmind** constructor. This is an optio
 
 ## addMutationListener
 
-It is possible to listen to all mutations performed in Overmind. This allows you to create special effects based on mutations within a certain domain of your app, or whatever else you come up with.
+It is possible to listen to all mutations performed in Overmind. This allows you to create special effects based on mutations within a certain domain of your app, or whatever else you come up with. Note that this method triggers instantly when the mutation occurs, you might rather want to use **addFlushListener** to be notified about batched changes, like the components does.
 
 ```marksy
 h(Example, { name: "api/app_addMutationListener" })