README: Add CONFIG_SPI_FLASH_DATAFLASH description

This patch adds CONFIG_SPI_FLASH_DATAFLASH descrition on README
file for more readble for users.

Signed-off-by: Jagan Teki <jteki@openedev.com>
diff --git a/README b/README
index 168d824..c49af74 100644
--- a/README
+++ b/README
@@ -3099,6 +3099,11 @@
 		is needed for subsystems like UBI which can only operate on top
 		of the MTD layer.
 
+		CONFIG_SPI_FLASH_DATAFLASH	SPI based Dataflash
+
+		Define this option to access AT45xxx Dataflash chips support
+		using spi flash interface.
+
 - SystemACE Support:
 		CONFIG_SYSTEMACE