Some tweaks to the staticfiles docs to clarify things for new users. Thanks...

Some tweaks to the staticfiles docs to clarify things for new users. Thanks Jannis and brutasse for review and discussion.

* Rearranged 'in a nutshell' usage docs to clarify app-dirs vs STATICFILES_DIRS, initially focus on the simplest path to working local dev, and remove the need for repetitive 'you don't need this in local dev' notes.
* Added docs on using staticfiles serve view for non-staticfiles (e.g. user-uploaded files).

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15380 bcc190cf-cafb-0310-a4f2-bffc1f526a37