Fix readme.

I used a modified nandsim but to use an unmodified kernel ubiattach is
needed instead.

README

@@ -55,7 +55,13 @@ sudo modprobe nandsim first_id_byte=0x2c second_id_byte=0xf1 third_id_byte=0x80
 # mlc nand chip. Fails ubi
 sudo modprobe nandsim first_id_byte=0x20 second_id_byte=0xaa third_id_byte=0x0c fourth_id_byte=0x15 parts=8,40,40,5,5
 
+# not that for ubi to work with images for ARM targets you can not use this modprobe without fixing nandsim
 sudo modprobe ubi mtd=5
+
+#alternative way
+sudo modprobe ubi
+sudo ubiattach -p /dev/mtd5 -O 2048
+
 sudo modprobe ubifs
  
 sudo ubimkvol /dev/ubi0 -N "rootfs_0" -s 60MiB