index: add ledge doc

Add the ledge doc from the oniro repo.

Signed-off-by: Marta Rybczynska <marta.rybczynska@linaro.org>

index.rst

@@ -75,6 +75,7 @@ daily life.
    oniro/supported-technologies/containers
    oniro/supported-technologies/modbus
    oniro/supported-technologies/lvgl
+   oniro/supported-technologies/ledge
 
 .. toctree::
    :caption: Supported Toolchains