cmd/benchfilter: use correct doc link anchor

Change-Id: I90831c657712dd705b95fe3437d279ca54844f62
Reviewed-on: https://go-review.googlesource.com/c/perf/+/471635
Auto-Submit: Michael Pratt <mpratt@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
diff --git a/cmd/benchfilter/main.go b/cmd/benchfilter/main.go
index 5ede808..a1c8bb5 100644
--- a/cmd/benchfilter/main.go
+++ b/cmd/benchfilter/main.go
@@ -28,7 +28,7 @@
 provided, it reads from stdin.
 
 The filter language is described at
-https://pkg.go.dev/golang.org/x/perf/cmd/benchstat#Filtering
+https://pkg.go.dev/golang.org/x/perf/cmd/benchstat#hdr-Filtering
 `)
 	flag.PrintDefaults()
 }