runtime(doc): Fix an omission in the documentation.

closes: #16960

Signed-off-by: Christian Brabandt <cb@256bit.org>

Author: cvwillegen

runtime/doc/builtin.txt

@@ -1,4 +1,4 @@
-*builtin.txt*	For Vim version 9.1.  Last change: 2025 Mar 23
+*builtin.txt*	For Vim version 9.1.  Last change: 2025 Mar 24
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -5896,8 +5896,8 @@ indexof({object}, {expr} [, {opts}])			*indexof()*
 		v:true.  {object} must be a |List|, a |Tuple| or a |Blob|.
 
 		If {object} is a |List| or a |Tuple|, evaluate {expr} for each
-		item in the List until the expression is v:true and return the
-		index of this item.
+		item in the List or Tuple until the expression is v:true
+		and return the index of this item.
 
 		If {object} is a |Blob| evaluate {expr} for each byte in the
 		Blob until the expression is v:true and return the index of