sandbox: Update minor documentation changes

- Use _defconfig instead of _config, but still _config is working.
- Corrected README.sandbox path in ./README

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index 0a0f528..276869a 100644
--- a/README
+++ b/README
@@ -272,7 +272,7 @@
 specific to be undertaken on a native platform. The sandbox is also used to
 run some of U-Boot's tests.
 
-See board/sandbox/sandbox/README.sandbox for more details.
+See board/sandbox/README.sandbox for more details.
 
 
 Configuration Options:
diff --git a/board/sandbox/README.sandbox b/board/sandbox/README.sandbox
index 529c447..5f879f5 100644
--- a/board/sandbox/README.sandbox
+++ b/board/sandbox/README.sandbox
@@ -19,7 +19,7 @@
 CONFIG_SANDBOX is defined when building a native board.
 
 The chosen vendor and board names are also 'sandbox', so there is a single
-board in board/sandbox/sandbox.
+board in board/sandbox.
 
 CONFIG_SANDBOX_BIG_ENDIAN should be defined when running on big-endian
 machines.
@@ -32,7 +32,7 @@
 
 To run sandbox U-Boot use something like:
 
-   make sandbox_config all
+   make sandbox_defconfig all
    ./u-boot
 
 Note:
@@ -41,7 +41,7 @@
    build sandbox without SDL (i.e. no display/keyboard support) by removing
    the CONFIG_SANDBOX_SDL line in include/configs/sandbox.h or using:
 
-      make sandbox_config all NO_SDL=1
+      make sandbox_defconfig all NO_SDL=1
       ./u-boot