docs: Reworded comments for the new credit types filter

PiperOrigin-RevId: 341478628

google/cloud/billing/budgets/v1beta1/budget_model.proto

@@ -187,13 +187,17 @@ message Filter {
   // Only zero or one project can be specified currently.
   repeated string projects = 1 [(google.api.field_behavior) = OPTIONAL];
 
-  // Optional. A list of credit types to be subtracted from gross cost to
-  // determine the spend for threshold calculations if and only if
-  // credit_types_treatment is INCLUDE_SPECIFIED_CREDITS. If
-  // credit_types_treatment is not INCLUDE_SPECIFIED_CREDITS, this field must be
-  // empty. See credits.type at
-  // https://cloud.google.com/billing/docs/how-to/export-data-bigquery-tables#data-schema
-  // for a list of acceptable credit type values in this field.
+  // Optional. If
+  // [Filter.credit_types_treatment][google.cloud.billing.budgets.v1beta1.Filter.credit_types_treatment]
+  // is INCLUDE_SPECIFIED_CREDITS, this is a list of credit types to be
+  // subtracted from gross cost to determine the spend for threshold
+  // calculations.
+  //
+  // If
+  // [Filter.credit_types_treatment][google.cloud.billing.budgets.v1beta1.Filter.credit_types_treatment]
+  // is **not** INCLUDE_SPECIFIED_CREDITS, this field must be empty. See [a list
+  // of acceptable credit type
+  // values](https://cloud.google.com/billing/docs/how-to/export-data-bigquery-tables#credits-type).
   repeated string credit_types = 7 [(google.api.field_behavior) = OPTIONAL];
 
   // Optional. If not set, default behavior is `INCLUDE_ALL_CREDITS`.