Update chapter07.rst


![screenshot at 2013-05-06 16 37 58](https://f.cloud.github.com/assets/737900/465682/85a02fb4-b63d-11e2-9d79-0715d3c7c200.png)

Changing the import from mysite.books to books.
I am getting an ImportError that books doesn't exist if I use mysite.books

Directory structure is
mysite/
   mysite/
      settings.py
      urls.py
      wsgi.py
   manage.py
   books/
     models.py
     tests.py
     views.py