Fix typo: commmand -> command.

Signed-off-by: Vagrant Cascadian <vagrant@debian.org>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>
diff --git a/doc/README.nand b/doc/README.nand
index 0ff5633..545d88c 100644
--- a/doc/README.nand
+++ b/doc/README.nand
@@ -94,7 +94,7 @@
 	address of u-boot MTD partition in NAND.
 
    CONFIG_CMD_NAND
-      Enables NAND support and commmands.
+      Enables NAND support and commands.
 
    CONFIG_CMD_NAND_TORTURE
       Enables the torture command (see description of this command below).