improved the example docs to help #303 

The example docs didn't make it obvious that the docker daemon was running in the background, I made it more obvious and added a page explaining how to run the examples.

The warning header on the examples needs to be styled, maybe @dhrp can help me with that. We have something we use on the dotcloud docs, so maybe we can use the same? See the warning on the top of http://docs.dotcloud.com/services/postgresql/

This is for #303