cgtqmx6eval: README: Fix parameter of 'sf write' command

'sf command' should receive the length in sector boundaries, so fix it
accordingly.

Also, show the steps to set the server and board IP addresses for
making the steps clearer.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>

board/congatec/cgtqmx6eval/README

@@ -25,11 +25,15 @@ host PC (/tftpboot , for example).
 
 => sf probe
 
+=> setenv serverip <server_ip_address>
+
+=> setenv ipaddr <board_ip_address>
+
 => tftp 0x12000000 SPL
 
 => sf erase 0x0 0x10000
 
-=> sf write 0x12000000 0x400 0x100
+=> sf write 0x12000000 0x400 0x10000
 
 => tftp 0x12000000 u-boot.img