Refs #23778 -- Fixed wording and newlines
Refs #23778 -- Moved runtests.py up in the hierarchy
Refs #23778 -- Removed extraneous conditional
Refs #23778 -- Removed now unecessary paragraph about sys.path
Refs #23778 -- Rewording in test_settings.py section

Removed reference to Django test code since it is not the best example to follow for
reusable apps.
Refs #23778 -- Added a section about test-only models.