Fixed #14627 -- Made Tutorial 3 more explicit regarding the transformations...

Fixed #14627 -- Made Tutorial 3 more explicit regarding the transformations the URLconf undergoes in the final two sections, and gave an example of concatenating two patterns() in the process. Thanks to filmer for the report.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14472 bcc190cf-cafb-0310-a4f2-bffc1f526a37