'Load sphinx_rtd_theme theme (if exists).'

def load_sphinx_rtd_theme(self):

    try:
        import sphinx_rtd_theme
        theme_path = sphinx_rtd_theme.get_html_theme_path()
        self.themes['sphinx_rtd_theme'] = path.join(theme_path, 'sphinx_rtd_theme')
    except ImportError:
        pass
