Update tutorial-use-custom-image-cli.md (Typo "a Azure"→"an Azure" )

Typo "A [Azure Compute Gallery]"→"An [Azure Compute Gallery]" 
https://learn.microsoft.com/en-us/azure/virtual-machine-scale-sets/tutorial-use-custom-image-cli
https://github.com/MicrosoftDocs/azure-docs/blob/main/articles/virtual-machine-scale-sets/tutorial-use-custom-image-cli.md
#PingMSFTDocs

Author: hyoshioka0128

articles/virtual-machine-scale-sets/tutorial-use-custom-image-cli.md

@@ -28,7 +28,7 @@ When you create a scale set, you specify an image to be used when the VM instanc
 - This article requires version 2.4.0 or later of the Azure CLI. If using Azure Cloud Shell, the latest version is already installed.
 
 ## Overview
-A [Azure Compute Gallery](../virtual-machines/shared-image-galleries.md) simplifies custom image sharing across your organization. Custom images are like marketplace images, but you create them yourself. Custom images can be used to bootstrap configurations such as preloading applications, application configurations, and other OS configurations.
+An [Azure Compute Gallery](../virtual-machines/shared-image-galleries.md) simplifies custom image sharing across your organization. Custom images are like marketplace images, but you create them yourself. Custom images can be used to bootstrap configurations such as preloading applications, application configurations, and other OS configurations.
 
 The Azure Compute Gallery lets you share your custom VM images with others. Choose which images you want to share, which regions you want to make them available in, and who you want to share them with.