docs: [batch] Clarify Batch only supports global custom instance temp…

…late now (#5726)

* docs: Clarify Batch only supports global custom instance template now

PiperOrigin-RevId: 680722756

Source-Link: googleapis/googleapis@42f7085

Source-Link: googleapis/googleapis-gen@8aafe35
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packages/google-cloud-batch/README.md

@@ -44,7 +44,7 @@ Google APIs Client Libraries, in [Client Libraries Explained][explained].
 1.  [Select or create a Cloud Platform project][projects].
 1.  [Enable billing for your project][billing].
 1.  [Enable the Batch API][enable_api].
-1.  [Set up authentication with a service account][auth] so you can access the
+1.  [Set up authentication][auth] so you can access the
     API from your local workstation.
 
 ### Installing the client library
@@ -199,4 +199,4 @@ See [LICENSE](https://github.com/googleapis/google-cloud-node/blob/main/LICENSE)
 [projects]: https://console.cloud.google.com/project
 [billing]: https://support.google.com/cloud/answer/6293499#enable-billing
 [enable_api]: https://console.cloud.google.com/flows/enableapi?apiid=batch.googleapis.com
-[auth]: https://cloud.google.com/docs/authentication/getting-started
+[auth]: https://cloud.google.com/docs/authentication/external/set-up-adc-local

packages/google-cloud-batch/protos/google/cloud/batch/v1/job.proto

@@ -423,7 +423,10 @@ message AllocationPolicy {
 
       // Name of an instance template used to create VMs.
       // Named the field as 'instance_template' instead of 'template' to avoid
-      // c++ keyword conflict.
+      // C++ keyword conflict.
+      //
+      // Batch only supports global instance templates.
+      // You can specify the global instance template as a full or partial URL.
       string instance_template = 2;
     }