n1sdp: Adding pre-required packages missing in an Ubuntu live server image

This patch adds the packages to the pre-requisite packages in the
user-guide.rst that are found missing while using an Ubuntu 20.04
live-server image in the host system.

Signed-off-by: Himanshu Sharma <Himanshu.Sharma@arm.com>
Change-Id: I9f01d21250a4301e706b4c4d641f5f47a4656fa8