Scanner daemon: update setup, updated README, virtualenv changes

Hi spl0k,

I finally tested the scanner_daemon branch. Works fine so far. :+1: 

I added supysonic-watcher to the list of scripts in the setup, updated the README with notes regarding the daemon configuration and the dependancy to watchdog.

Personally, I use virtualenv and thought it would be good idea to change the shebang lines to use /usr/bin/env.