"Editing Basics" first pass

I have more documentation/screenshots to add (covering things like the "Page" menu when editing a specific page, adding content/plugins, etc.) but this at least gets rid of the "TODOs" in the docs.
I think it's a wise choice to default to the dev version of Django's own docs. We don't know which version our users will be using, but we'll have to assume they can figure out how to select the correct version for themselves.