[media] add DVB documentation to Sphinx

Now that all DVB files got converted, add it to Sphinx
build.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
diff --git a/Documentation/index.rst b/Documentation/index.rst
index a5a100d..b61d8de 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -16,6 +16,7 @@
    kernel-documentation
    media/media_uapi
    media/media_drivers
+   media/dvb-drivers/index
 
 Indices and tables
 ==================