docs: prefix sudo to commands that need root privileges

Prefix sudo to commands that need root privileges. This is more accurate
and improves user experience.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Lijian Zhang <lijian.zhang@arm.com>
Reviewed-by: Nathan Brown <nathan.brown@arm.com>
Reviewed-by: Tianyu Li <tianyu.li@arm.com>

Change-Id: I1c480ab1ccb9cdb0a1f7ab04016908bb4968e7dc