doc: add sandbox API

Add sandbox API to generated HTML documentation

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/doc/api/index.rst b/doc/api/index.rst
index ae4a1b6..cbecd10 100644
--- a/doc/api/index.rst
+++ b/doc/api/index.rst
@@ -12,6 +12,7 @@
    linker_lists
    pinctrl
    rng
+   sandbox
    serial
    timer
    unicode
diff --git a/doc/api/sandbox.rst b/doc/api/sandbox.rst
new file mode 100644
index 0000000..7247763
--- /dev/null
+++ b/doc/api/sandbox.rst
@@ -0,0 +1,9 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+Sandbox
+=======
+
+The following API routines are used to implement the U-Boot sandbox.
+
+.. kernel-doc:: include/os.h
+   :internal: