DOC-9574: Add a note that N1QL can select any qualifying FTS index (#2490)

Author: abhinavdangeti

modules/fts/pages/fts-searching-from-N1QL.adoc

@@ -240,6 +240,11 @@ Order pushdown is possible only if query ORDER BY has only <<search_score>> on t
 Offset and Limit pushdown is possible if the query only has a SEARCH() predicate, using a single search index -- no IntersectScan or OrderIntersectScan.
 Group aggregates and projection are not pushed.
 
+[NOTE]
+--
+If the "index" setting isn't specified within the options argument of the _SEARCH_ function, N1QL can pick any FTS index available in the system that qualifies for the query. If a number of FTS indexes qualify, then one that is defined most precise will be chosen.
+--
+
 === Examples
 
 .Search using a query string

modules/n1ql/pages/n1ql-language-reference/searchfun.adoc

@@ -248,6 +248,11 @@ Order pushdown is possible only if query ORDER BY has only <<search_score>> on t
 Offset and Limit pushdown is possible if the query only has a SEARCH() predicate, using a single search index -- no IntersectScan or OrderIntersectScan.
 Group aggregates and projection are not pushed.
 
+[NOTE]
+--
+If the "index" setting isn't specified within the options argument of the _SEARCH_ function, N1QL can pick any FTS index available in the system that qualifies for the query. If a number of FTS indexes qualify, then one that is defined most precise will be chosen.
+--
+
 === Examples
 
 .Search using a query string