documentation: Give more details

Give more precise directions to the NXP documentation regarding the
installation of debugger dependencies.

Remove the instruction to add the ewaol user to the docker group as it
is already setup this way in the image.

Add a note about keeping the ROS_DOMAIN_ID clear.

Make the "SSH -X ..." command a required step.

Expand on the UART usage.

Add links to the concepts exposed in the introduction paragraph.

Add a note about expected Autoware error logs.

Issue-Id: SCM-5893
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>
Change-Id: I0acc60049238c8babe104ccd39d9e5c700a0a6fa