Address docs issues

Author: julian-elastic

docs/changelog/131559.yaml

@@ -1,5 +1,5 @@
 pr: 131559
-summary: Add support for Lookup Join on Multiple Fields
+summary: Add support for LOOKUP JOIN on multiple fields
 area: ES|QL
 type: enhancement
 issues: [ ]

docs/reference/query-languages/esql/esql-lookup-join.md

@@ -33,11 +33,14 @@ For example, you can use `LOOKUP JOIN` to:
 The `LOOKUP JOIN` command adds fields from the lookup index as new columns to your results table based on matching values in the join field.
 
 The command requires two parameters:
-- The name of the lookup index (which must have the `lookup` [`index.mode setting`](/reference/elasticsearch/index-settings/index-modules.md#index-mode-setting))
-- The name of the field to join on
-
+* The name of the lookup index (which must have the `lookup` [`index.mode setting`](/reference/elasticsearch/index-settings/index-modules.md#index-mode-setting))
+* The field(s) to join on. Can be either:
+  * A single field name
+  * A comma-separated list of field names {applies_to}`stack: ga 9.2`
+  
 ```esql
-LOOKUP JOIN <lookup_index> ON <field_name>
+LOOKUP JOIN <lookup_index> ON <field_name>  # Join on a single field
+LOOKUP JOIN <lookup_index> ON <field_name1>, <field_name2>, <field_name3>  # Join on multiple fields
 ```
 
 :::{image} ../images/esql-lookup-join.png