runtime(doc): clarify return type for findfile()/finddir()

closes: #17171

Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 7353776..70f3c88 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -3260,7 +3260,8 @@
 		Can also be used as a |method|: >
 			GetName()->finddir()
 <
-		Return type: |String|
+		Return type: list<string> if {count} is negative, |String|
+		otherwise
 
 
 findfile({name} [, {path} [, {count}]])				*findfile()*
@@ -3274,7 +3275,8 @@
 		Can also be used as a |method|: >
 			GetName()->findfile()
 <
-		Return type: |String|
+		Return type: list<string> if {count} is negative, |String|
+		otherwise
 
 
 flatten({list} [, {maxdepth}])					*flatten()*