docs: clarified where ordering_key will be written if write_metadata …

…is set

PiperOrigin-RevId: 551210991

google/pubsub/v1/pubsub.proto

@@ -1030,7 +1030,11 @@ message CloudStorageConfig {
   // Message payloads and metadata will be written to files as an Avro binary.
   message AvroConfig {
     // When true, write the subscription name, message_id, publish_time,
-    // attributes, and ordering_key as additional fields in the output.
+    // attributes, and ordering_key as additional fields in the output. The
+    // subscription name, message_id, and publish_time fields are put in their
+    // own fields while all other message properties other than data (for
+    // example, an ordering_key, if present) are added as entries in the
+    // attributes map.
     bool write_metadata = 1;
   }