doc: Adding new network & local usb deployment

As per the previous commits :
6d242eb808e35947bfa09c3c49cc64c92d8734e6
16209eadf28c55aa0e278be3ff96b6fc82e2ac33
560b877b10c510edc1bc5a23e0951fb8f13fe49c

Two new features got added :
- being able to deploy a system using a usb stick with no network and no
  edeploy server
- being able to deploy withotu any DHCP server and no PXE server.

This patch add the documentation about those features.