chore: native rendering datasource information.

native-rendering/documents-designer/data-source.md

@@ -14,6 +14,15 @@ or the bracket notation:
 ```code
 $['shipment']['tracking_number']
 ```
+
+For each document you need to select DataSource property value:
+* **package** -  prints a label for each package in the shipment;
+* **shipment** - prints only one label for the whole shipment.
+
+![Data Source](./images/data-source.png)
+ 
+
+
 ## Restrictions
 1. Root element starts from `$.` or `.`
 2. Nested object path have to start from `.` If nested object starts from `$.` it means reference to root element. In this case no relation will be considered.
@@ -83,7 +92,7 @@ $.shipment.metadata['account.number']
 
 #### Current package reference
 
-You can also reference to the current *Package* using prefix `@`
+If you select **package** as DataSource, you can also refer to the current *Package* using prefix `@`
 
 ```code
 @package.weight_details.weight_in_grams