autotest: Mention that Django 1.5 is the currently supported version

And that installs won't work in other versions. Try to
make that abundantly clear through docs and install script.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #872 from autotest/django-15-notice

autotest: Mention that Django 1.5 is the currently supported version