Fix typo

[riparuk]

I think it was a typo, autosize from fit_text() method should be NONE. I'm a newbie and want to ask what is the analysis section in docs? is it only for the development section? I'm playing around with python-pptx right now and need an approach to shape and/or size text that can be dynamic, is autofit_text a feature that doesn't exist yet and is being developed?