Add link to AWS Docs to Wiki

[mjgiancola]

First, I am extremely appreciative that the section Warming up the disk is on the wiki; it saved me a big headache. However, there is a more complete guide on the AWS Docs that was useful to me & would likely be useful to others. Most significantly, it shows how to list the devices on your instance in order to point dd at the correct device (my device wasn't xvda, so the command in the wiki didn't work for me).