_content/security/fuzz: tweak example for running file2fuzz

When running file2fuzz without any arguments it will read from stdin.
This might confuse users who copy the commands from the example,
expecting something to happen. Suggest running it with -h instead.

Change-Id: I50cc776af66af5126fb283dee228df644c6e340d
Reviewed-on: https://go-review.googlesource.com/c/website/+/401954
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Auto-Submit: Dominik Honnef <dominik@honnef.co>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Dominik Honnef <dominik@honnef.co>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
diff --git a/_content/security/fuzz/index.md b/_content/security/fuzz/index.md
index adf892a..1c501b1 100644
--- a/_content/security/fuzz/index.md
+++ b/_content/security/fuzz/index.md
@@ -245,7 +245,7 @@
 
 ```
 $ go install golang.org/x/tools/cmd/file2fuzz@latest
-$ file2fuzz
+$ file2fuzz -h
 ```
 
 ## Resources