Update description

Author: wchen-r7

modules/exploits/osx/browser/safari_user_assisted_applescript_exec.rb

@@ -21,6 +21,9 @@ def initialize(info = {})
         additional confirmation from the user. By getting the user to press
         cmd-R in Safari, and by hooking the cmd-key keypress event, a user
         can be tricked into running arbitrary Applescript code.
+
+        Gatekeeper should be disabled from Security & Privacy in order to
+        avoid the unidentified Developer prompt.
       },
       'License'         => MSF_LICENSE,
       'Arch'            => ARCH_CMD,