index: Include new Matter documentation

The actual documentation was added in the Oniro repo. The new file need
to be added here as well to produce a working documentation build.

Signed-off-by: Stefan Schmidt <stefan.schmidt@huawei.com>

index.rst

@@ -71,6 +71,7 @@ daily life.
    :maxdepth: 2
 
    oniro/supported-technologies/openthread
+   oniro/supported-technologies/matter
    oniro/supported-technologies/containers
    oniro/supported-technologies/modbus
    oniro/supported-technologies/lvgl