chore(docs): make it more awesome

* cleanup Heroku deploy instructions.
* `collectstatic` is run automatically by Heroku, it's no longer needed.
* include 'getting started' section in generated code too.
* add `createsuperuser` explicity, as `migrate` will not add them by default. (Until it's fixed in https://github.com/pydanny/cookiecutter-django/issues/39)