Update documentation

docs/create-image-and-azure-resources.md

@@ -75,7 +75,7 @@ In any case, you will need these software installed:
 ## Manual image generation
 
 This repository includes a script that assists in generating images in Azure.
-All you need is an Azure subscription and a build agent configured as described above.
+All you need is an Azure subscription, a resource group in that subscription and a build agent configured as described above.
 We suggest starting with building the UbuntuMinimal image because it includes only basic software and builds in less than 30 minutes.
 
 All the commands below should be executed in PowerShell.
@@ -96,7 +96,8 @@ Import-Module .\helpers\GenerateResourcesAndImage.ps1
 Finally, run the `GenerateResourcesAndImage` function, setting the mandatory arguments: image type and where to build and store the resulting managed image:
 
 - `SubscriptionId` - your Azure Subscription ID;
-- `ResourceGroupName` - the name of the resource group that will be created within your subscription (e.g., "imagegen-test");
+- `ResourceGroupName` - the name of the resource group that will store the resulting artifact (e.g., "imagegen-test").
+    The resource group must already exist in your Azure subscription;
 - `AzureLocation` - the location where resources will be created (e.g., "East US");
 - `ImageType` - the type of image to build (we suggest choosing "UbuntuMinimal" here; other valid options are "Windows2019", "Windows2022", "Windows2025", "Ubuntu2004", "Ubuntu2204", "Ubuntu2404").
 
@@ -195,9 +196,10 @@ you can use Packer directly. To do this, you will need:
 - a resource group created in your Azure subscription where the managed image will be stored;
 - a string to be used as a password for the user used to install software (Windows only).
 
-Then, you can invoke Packer in your CI/CD pipeline using the following command:
+Then, you can invoke Packer in your CI/CD pipeline using the following commands:
 
 ```powershell
+packer plugins install github.com/hashicorp/azure 2.2.1
 packer build -var "subscription_id=$SubscriptionId" `
              -var "client_id=$ClientId" `
              -var "client_secret=$ClientSecret" `

helpers/GenerateResourcesAndImage.ps1

@@ -83,7 +83,7 @@ Function GenerateResourcesAndImage {
         .PARAMETER SubscriptionId
             The Azure subscription id where the Azure resources will be created.
         .PARAMETER ResourceGroupName
-            The name of the resource group to create the Azure resources in.
+            The name of the resource group to store the resulting artifact. Resource group must already exist.
         .PARAMETER ImageType
             The type of image to generate. Valid values are: Windows2019, Windows2022, Windows2025, Ubuntu2004, Ubuntu2204, Ubuntu2404, UbuntuMinimal.
         .PARAMETER ManagedImageName