'Return a string giving help on how to customize this plugin.
By default raise a :class:`NotImplementedError`, which indicates that
the plugin does not require customization.
If you re-implement this method in your subclass, the user will
be asked to enter a string as customization for this plugin.
The customization string will be available as
``self.site_customization``.
Site customization could be anything, for example, the path to
a needed binary on the user\'s computer.
:param gui: If True return HTML help, otherwise return plain text help.'

def customization_help(self, gui=False):

    raise NotImplementedError
