update NavigationActions reference

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 the `NavigationActions` don't throw errors or anything when they are unhandled ( similar to how when you dispatch an action that isn't handled by a reducer in redux and nothing happens ). However, if the app state doesn't change as a result of dispatch then the return value for dispatch is `false` and `true` otherwise.
+
 The following actions are supported:
 
 * [Navigate](#navigate) - Navigate to another route