added instructions for getting the example projects running to the 'SETUP' section of contributing.rst

When you clone the repo, there are two example projects using djadmin2, but if you try to run them, you get a "djadmin2 is not found" error.  I resolved this by creating a symlink in my example directory, but there are other, possibly better ways, such as adding djadmin2 to your sys.path.

I also added the standard "create databse" and "runserver" stuff.