docs: clarify that subscription_id provider property is required fo…

…r plan/apply

website/docs/index.html.markdown

@@ -103,14 +103,16 @@ The following arguments are supported:
 
 * `features` - (Required) A `features` block as defined below which can be used to customize the behaviour of certain Azure Provider resources.
 
+* `subscription_id` - (Required) The Subscription ID which should be used. This can also be sourced from the `ARM_SUBSCRIPTION_ID` Environment Variable.
+
+-> The `subscription_id` property is required when performing a plan or apply operation, but is not required to run `terraform validate`.
+
 * `client_id` - (Optional) The Client ID which should be used. This can also be sourced from the `ARM_CLIENT_ID` Environment Variable.
 
 * `client_id_file_path` (Optional) The path to a file containing the Client ID which should be used. This can also be sourced from the `ARM_CLIENT_ID_FILE_PATH` Environment Variable.
 
 * `environment` - (Optional) The Cloud Environment which should be used. Possible values are `public`, `usgovernment`, `german`, and `china`. Defaults to `public`. This can also be sourced from the `ARM_ENVIRONMENT` Environment Variable. Not used when `metadata_host` is specified.
 
-* `subscription_id` - (Optional) The Subscription ID which should be used. This can also be sourced from the `ARM_SUBSCRIPTION_ID` Environment Variable.
-
 * `tenant_id` - (Optional) The Tenant ID which should be used. This can also be sourced from the `ARM_TENANT_ID` Environment Variable.
 
 * `auxiliary_tenant_ids` - (Optional) List of auxiliary Tenant IDs required for multi-tenancy and cross-tenant scenarios. This can also be sourced from the `ARM_AUXILIARY_TENANT_IDS` Environment Variable.
@@ -228,4 +230,4 @@ To view the latest specific Azure Resource Providers included in each set, pleas
 
 In addition to, or in place of, the sets described above, you can also configure the AzureRM Provider to register specific Azure Resource Providers, by setting the `resource_providers_to_register` provider property. This should be a list of strings, containing the exact names of Azure Resource Providers to register. For a list of all resource providers, please refer to [official Azure documentation](https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-providers-and-types).
 
-->**Note on Permissions** The User, Service Principal or Managed Identity running Terraform should have permissions to register [Azure Resource Providers](https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-providers-and-types). If the principal running Terraform has insufficient permissions to register Resource Providers then we recommend setting the property [`resource_provider_registrations`](#resource_provider_registrations) to `none` in the provider block to prevent auto-registration.
+-> **Note on Permissions** The User, Service Principal or Managed Identity running Terraform should have permissions to register [Azure Resource Providers](https://learn.microsoft.com/en-us/azure/azure-resource-manager/management/resource-providers-and-types). If the principal running Terraform has insufficient permissions to register Resource Providers then we recommend setting the property [`resource_provider_registrations`](#resource_provider_registrations) to `none` in the provider block to prevent auto-registration.