Documentation fixes on topics logging - add code-block and fix 3 spaces indentation

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That makes sense! 
but then there is many place where we use ```.. code-block:: python``` where we should not want to, for intance on the example ```class Command(BaseCommand```: https://docs.djangoproject.com/en/1.7/howto/custom-management-commands/ 
if the example break we won't know and it's also more verbose.