Clarify in documentation that setting a vote matches with "commentby"

Release-Notes: skip
Google-Bug-Id: b/249180214
Change-Id: Ife43a75c7ac2c787ff5edbd4001992c9b131937c
diff --git a/Documentation/user-search.txt b/Documentation/user-search.txt
index 606bf74..1c4750b 100644
--- a/Documentation/user-search.txt
+++ b/Documentation/user-search.txt
@@ -618,7 +618,7 @@
 +
 Changes containing a top-level or inline comment by 'USER'. The special
 case of `commentby:self` will find changes where the caller has
-commented.
+commented. Note that setting a vote is also considered as a comment.
 
 [[from]]
 from:'USER'::