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