Added DOS vulnerability

Added a sleep to the show messages page to show how using slow blocking
methods can allow DOS to occur.

app/controllers/messages_controller.rb

@@ -3,6 +3,8 @@ class MessagesController < ApplicationController
   def index
     @messages = current_user.messages
     @message = Message.new
+    # Blocking code can cause DOS
+    sleep(3)
   end
 
   def show