Updates user guide following out of box testing.
Updates user guide following out of box testing.

Change-Id: I0cd355d9fc7f14fb4eabb443d596d6f0858f609e
Signed-off-by: Eleanor Bonnici <3bb47669a1d3c49f63950fe2fc971fc33b9b82f9@arm.com>

lsigithub/arm-trusted-firmware_public,achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public