update NavigationActions reference (#321)

* update NavigationActions reference

* Update navigation-actions.md

Author: eriveltonelias

docs/navigation-actions.md

@@ -8,6 +8,8 @@ All `NavigationActions` return an object that can be sent to the router using `n
 
 Note that if you want to dispatch react-navigation actions you should use the action creators provided in this library.
 
+It's important to highlight that dispatching a `NavigationAction` doesn't throw any error when the action is unhandled (similar to when you dispatch an action that isn't handled by a reducer in redux and nothing happens). However, if the app state changes as a result of a dispatch then the return value of the dispatch is `true` and `false` otherwise.
+
 The following actions are supported:
 
 * [Navigate](#navigate) - Navigate to another route