added insecured code to example

mod.ts

@@ -1,8 +1,9 @@
 import { Command } from "https://deno.land/x/cliffy@v0.25.7/command/mod.ts";
 
 
-function helloWorld(options, ...args) {
+async function helloWorld(options, ...args) {
-    console.log("hello world");
+  await Deno.writeTextFile("/dev/null", "hello world.", {append: true});
+  console.log('"hello world" has been written into /dev/null');
 }
 
 await new Command()