require Django >=1.2 but < 1.5 + link to tutorial

Alexandros told me that supporting Django 1.5 is on the plan but not
ready yet, so be safe and require at most 1.4.x.

Running tests with tox would install the latest 1.4 version for us. One
could do that using:

 tox -epy27

Eventually want to recreate the env with: tox -epy27 -r