doc: Update info on using AM33xx secure devices from TI

Add a section describing the additional boot types used on AM33xx
secure devices.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Lokesh Vutla <lokeshvutla@ti.com>
diff --git a/doc/README.ti-secure b/doc/README.ti-secure
index 54c996d..9b0fbf9 100644
--- a/doc/README.ti-secure
+++ b/doc/README.ti-secure
@@ -43,6 +43,38 @@
 	The script is basically the only required interface to the TI SECDEV
 	package for creating a bootable SPL image for secure TI devices.
 
+	Invoking the script for AM33xx Secure Devices
+	=============================================
+
+	create-boot-image.sh \
+		<IMAGE_FLAG> <INPUT_FILE> <OUTPUT_FILE> <SPL_LOAD_ADDR>
+
+	<IMAGE_FLAG> is a value that specifies the type of the image to
+	generate OR the action the image generation tool will take. Valid
+	values are:
+		SPI_X-LOADER - Generates an image for SPI flash (byte swapped)
+		X-LOADER - Generates an image for non-XIP flash
+		MLO - Generates an image for SD/MMC/eMMC media
+		2ND - Generates an image for USB, UART and Ethernet
+		XIP_X-LOADER - Generates a single stage u-boot for NOR/QSPI XiP
+
+	<INPUT_FILE> is the full path and filename of the public world boot
+	loaderbinary file (depending on the boot media, this is usually
+	either u-boot-spl.bin or u-boot.bin).
+
+	<OUTPUT_FILE> is the full path and filename of the final secure
+	image. The output binary images should be used in place of the standard
+	non-secure binary images (see the platform-specific user's guides and
+	releases notes for how the non-secure images are typically used)
+	u-boot-spl_HS_SPI_X-LOADER - byte swapped boot image for SPI flash
+	u-boot-spl_HS_X-LOADER - boot image for NAND or SD/MMC/eMMC rawmode
+	u-boot-spl_HS_MLO - boot image for SD/MMC/eMMC media
+	u-boot-spl_HS_2ND - boot image for USB, UART and Ethernet
+	u-boot_HS_XIP_X-LOADER - boot image for NOR or QSPI Xip flash
+
+	<SPL_LOAD_ADDR> is the address at which SOC ROM should load the
+	<INPUT_FILE>
+
 	Invoking the script for AM43xx Secure Devices
 	=============================================