index.rst: Pull in the containers documentation

`oniro` introduced support and the associated documentation for
containers. Pull it into the aggregated Oniro docs.

Fixes: #157



Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

index.rst

@@ -72,6 +72,7 @@ daily life.
 
    meta-openharmony/supported-technologies/openharmony
    oniro/supported-technologies/openthread
+   oniro/supported-technologies/containers
 
 .. toctree::
    :caption: Troubleshoot