Update pattern_text documentation with new index sort setting

Author: jordan-powers

docs/reference/elasticsearch/mapping-reference/pattern-text.md

@@ -43,14 +43,16 @@ In both cases, all queries return a constant score of 1.0.
 
 ## Index sorting for improved compression
 The compression provided by `pattern_text` can be significantly improved if the index is sorted by the `template_id` field.
-For example, a typical approach would be to sort first by `message.template_id`, then by `@timestamp`, as shown in the following example.
+This sorting is not applied by default, but can be enabled for the `message` field of logs-mode indices (assuming it is of type `pattern_text`) by setting the index setting `index.logsdb.default_sort_on_message_template` to `true`.
+This will cause the index to be sorted by `hostname` (if present), then `message.template_id`, and finally by `@timestamp`.
+If the index is not logs-mode or the `pattern_text` field is named something other than `message`, index sorting can still be manually applied as shown in the following example.
 
 ```console
 PUT logs
 {
   "settings": {
     "index": {
-      "sort.field": [ "message.template_id", "@timestamp" ],
+      "sort.field": [ "notice.template_id", "@timestamp" ],
       "sort.order": [ "asc", "desc" ]
     }
   },
@@ -59,7 +61,7 @@ PUT logs
       "@timestamp": {
         "type": "date"
       },
-      "message": {
+      "notice": {
         "type": "pattern_text"
       }
     }