Add information about the field= operator

Author: JV0812

docs/search/search-query-language/search-operators/fields.md

@@ -6,6 +6,10 @@ sidebar_label: fields
 
 The `fields` operator allows you to specify which fields to display and their order in the results of a query. Use a fields operator to reduce the "clutter" of a search output that contains fields that aren't completely relevant to your query.
 
+:::info
+Using the `fields` operator includes both the specified fields and the default fields (from built-in sources and FERs). However, when `fields =` is used, only the specified fields are included in the query results.
+:::
+
 There are two fields operator modes:
 
 * Allowlist - only the fields included are kept in the search output.