Add env vars describing U-Boot target board

This can be useful for generic scripts. For example, rather than hard-
coding a script to ext2load tegra-harmony.dtb, it could load
${soc}-${board}.dtb and hence not need adjustments to run on multiple
boards.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/README b/README
index bb1b725..dac46f3 100644
--- a/README
+++ b/README
@@ -2229,6 +2229,20 @@
 		the environment like the "source" command or the
 		boot command first.
 
+		CONFIG_ENV_VARS_UBOOT_CONFIG
+
+		Define this in order to add variables describing the
+		U-Boot build configuration to the default environment.
+		These will be named arch, cpu, board, vendor, and soc.
+
+		Enabling this option will cause the following to be defined:
+
+		- CONFIG_SYS_ARCH
+		- CONFIG_SYS_CPU
+		- CONFIG_SYS_BOARD
+		- CONFIG_SYS_VENDOR
+		- CONFIG_SYS_SOC
+
 - DataFlash Support:
 		CONFIG_HAS_DATAFLASH