docs/orangepi: Add instructions for resizing SD image to power of two

docs/orangepi: Add instructions for resizing SD image to power of two

SD cards need to have a size of a power of two.
Update the Orange Pi machine documentation to include
instructions for resizing downloaded images using the
qemu-img command.

Signed-off-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200712183708.15450-1-nieklinnenbank@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
(cherry picked from commit 1c2329b5d644bad16e888d095e2021ad682201d9)
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>