Update build-a-hello-world-extension.md

Author: panjkov

docs/spfx/extensions/get-started/build-a-hello-world-extension.md

@@ -65,14 +65,16 @@ You can also follow the steps in this article by watching the video on the Share
 1. Open **./src/extensions/helloWorld/HelloWorldApplicationCustomizer.manifest.json**.
 
     This file defines your extension type and a unique identifier for your extension. You’ll need this ID later when you debug and deploy your extension to SharePoint.
+    
+    ![Application Customizer manifest json content](../../../images/ext-app-vscode-manifest.png)
 
 ## Code your Application Customizer
 
 Open the **./src/extensions/helloWorld/HelloWorldApplicationCustomizer.ts** file.
 
 Notice that base class for the Application Customizer is imported from the **\@microsoft/sp-application-base** package, which contains SharePoint framework code required by the Application Customizer.
 
-![Application Customizer manifest json content](../../../images/ext-app-vscode-manifest.png)
+![Application Customizer imports and inheritance](../../../images/ext-app-base.png)
 
 The logic for your Application Customizer is contained in the `onInit()` method, which is called when the client-side extension is first activated on the page. This event occurs after `this.context` and `this.properties` are assigned. As with web parts, `onInit()` returns a promise that you can use to do asynchronous operations.