fix: Fix TopNRowNumber documentation about spilling (facebookincubato…

…r#11569)

Summary: Pull Request resolved: facebookincubator#11569

Reviewed By: xiaoxmeng

Differential Revision: D66239359

Pulled By: Yuhta

fbshipit-source-id: 84084f834031866e3b497bc8ba6d8d84bab3d288

velox/docs/develop/operators.rst

@@ -950,7 +950,7 @@ assigns row numbers within each partition starting from 1.
 
 This operator accumulates state: a hash table mapping partition keys to a list
 of top 'limit' rows within that partition.  Returning the row numbers as
-a column in the output is optional. This operator doesn't support spilling yet.
+a column in the output is optional. This operator supports spilling as well.
 
 This operator is logically equivalent to a WindowNode followed by
 FilterNode(row_number <= limit), but it uses less memory and CPU.