streamline install guide

Hi Kamisama,

we recently updated our cake-resque plugin and found some mismatches in the [installation-docs](http://cakeresque.kamisama.me/install#install):

* The perform-Method does not match the "Final AppShell.php" section
* The described "$this->loadTasks();" is done directly within the initialize-Method of Shell.php

Let me know if both of the described issues are fine for you!