Added an introduction section

When I first read the documentation, I was confused about the relationship between the different sections of it (the documentation.) I think this introduction can help others get the big picture.

Author: Bilal-Abdeen

website/docs/docs/getting-started.md

@@ -11,6 +11,11 @@ We also assume you use `react-native@60.x.x` and above.
 
 For older versions, visit this [installation guide](https://github.com/wix/react-native-notifications/blob/v2/docs/installation.md).
 
+## Introduction 
+This library supports 2 kinds of motifications. 
+1. Local Notifications: These notifications are sent by an application to the device, on which it is running. The notification never leaves the device, on which the application is running. For more details on using these notification, please, refer to [Local Notifications](https://github.com/wix/react-native-notifications/edit/master/website/docs/docs/localNotifications.md) 
+2. Push Notifications. These notifications are sent by an application to any device through a communication server. For push notifications to work, you need to (1) register the devices, which can receive notifications, and (2) setup notification listeneres on these devices. To register devices, please refer to [Subscription](https://github.com/wix/react-native-notifications/blob/master/website/docs/docs/subscription.md). To setup notification listeneres, please refer to [Events](https://github.com/wix/react-native-notifications/blob/master/website/docs/docs/notifications-events.md). 
+
 ## Add react-native-notifications to your dependencies
 
 <Tabs