cmd/compilebench: update example to use benchcmp instead of benchstat

Change-Id: Id59ee04aba4d7c50e3b7c4e0b7e9aa75955640f5
Reviewed-on: https://go-review.googlesource.com/41861
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

cmd/compilebench/main.go

diff --git a/cmd/compilebench/main.go b/cmd/compilebench/main.go
index e04bd61..3ab2056 100644
--- a/cmd/compilebench/main.go
+++ b/cmd/compilebench/main.go
@@ -61,7 +61,7 @@
 //
 //	compilebench -count 10 -compile $(toolstash -n compile) >old.txt
 //	compilebench -count 10 >new.txt
-//	benchstat old.txt new.txt
+//	benchcmp old.txt new.txt
 //
 package main