Updating logging docs

This is an update to the centralized logging section of the docs. 

With the merge of PR Binstar/binstar.org#177 this refactored the logging script to a single command.

Considerations:

The logging script requires **sudo** But it is installed with `binstar-server`, thus the logging script has to be run after the header *Perform as Binstar User*. The instructions account for this.

Perhaps the instructions need to be refactored?

cc @LilaHickey @tpowellcio