Add python example documentation for LegacyViewingPipeline

On this page: https://opencolorio.readthedocs.io/en/latest/guides/developing/developing.html
extend the example to include python code from here:
https://opencolorio.org/old/developers/usage_examples.html
in the section "Displaying an image, using the CPU (Full Display Pipeline)."

The python binding to be demonstrated is here:
/usr/local/workspace/OpenColorIO-personal/src/bindings/python/apphelpers/PyLegacyViewingPipeline.cpp
See also:
/usr/local/workspace/OpenColorIO-personal/tests/python/LegacyViewingPipelineTest.py

Apri la pagina developing/developing.html e individua la sezione "Displaying an image, using the CPU (Full Display Pipeline)." Confronta l’esempio precedente in usage_examples.html con src/bindings/python/apphelpers/PyLegacyViewingPipeline.cpp e tests/python/LegacyViewingPipelineTest.py, quindi estendi la documentazione attuale con l’esempio Python e verifica che corrisponda al comportamento del binding.

Scritto dal modello di indicizzazione a partire dal testo della issue.