docs: update comments on ServiceAccount email and scopes fields

PiperOrigin-RevId: 623205186

google/cloud/batch/v1/job.proto

@@ -514,7 +514,17 @@ message AllocationPolicy {
   // Only instances[0] is supported now.
   repeated InstancePolicyOrTemplate instances = 8;
 
-  // Service account that VMs will run as.
+  // Defines the service account for Batch-created VMs. If omitted, the [default
+  // Compute Engine service
+  // account](https://cloud.google.com/compute/docs/access/service-accounts#default_service_account)
+  // is used. Must match the service account specified in any used instance
+  // template configured in the Batch job.
+  //
+  // Includes the following fields:
+  //  * email: The service account's email address. If not set, the default
+  //  Compute Engine service account is used.
+  //  * scopes: Additional OAuth scopes to grant the service account, beyond the
+  //  default cloud-platform scope. (list of strings)
   ServiceAccount service_account = 9;
 
   // Labels applied to all VM instances and other resources
@@ -624,13 +634,9 @@ message TaskGroup {
 
 // Carries information about a Google Cloud service account.
 message ServiceAccount {
-  // Email address of the service account. If not specified, the default
-  // Compute Engine service account for the project will be used. If instance
-  // template is being used, the service account has to be specified in the
-  // instance template and it has to match the email field here.
+  // Email address of the service account.
   string email = 1;
 
-  // List of scopes to be enabled for this service account on the VM, in
-  // addition to the cloud-platform API scope that will be added by default.
+  // List of scopes to be enabled for this service account.
   repeated string scopes = 2;
 }