README: Add CONFIG_SPL_OS_BOOT to README

Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/README b/README
index 7b5d01b..f39accf 100644
--- a/README
+++ b/README
@@ -3254,6 +3254,10 @@
 		supports MMC, NAND and YMODEM loading of U-Boot and NAND
 		NAND loading of the Linux Kernel.
 
+		CONFIG_SPL_OS_BOOT
+		Enable booting directly to an OS from SPL.
+		See also: doc/README.falcon
+
 		CONFIG_SPL_DISPLAY_PRINT
 		For ARM, enable an optional function to print more information
 		about the running system.