Update installation guide

Several small updates to the installation guide

* Remove the *downgrade ruby* step. That bug has been fixed.
* Use the *service xxx start* syntax instead of */etc/init.d/xxx start*
* Added a dns server to the demo network
* Added a step to enable backups to be made.
Ok, let's do "--snip--" then. I don't really have an opinion on the matter. :)