Add note that trigger_template is required.

Author: rileykarson

products/cloudbuild/terraform.yaml

@@ -28,6 +28,9 @@ overrides: !ruby/object:Overrides::ResourceOverrides
         name: 'trigger_id'
       build.steps: !ruby/object:Overrides::Terraform::PropertyOverride
         name: 'step'
+      triggerTemplate: !ruby/object:Overrides::Terraform::PropertyOverride
+        description: |
+          {{description}}This field is required, and will be corrected in 3.0.0.
       triggerTemplate.projectId: !ruby/object:Overrides::Terraform::PropertyOverride
         default_from_api: true
     custom_code: !ruby/object:Provider::Terraform::CustomCode