Merge pull request #3 from edx/will/clarify-travis

Clarify the purpose of setup.py in Travis

.travis.yml

 language: python
 python:
   - "2.7"
-before_script:
+install:
   - "pip install -r requirements.txt"
   - "pip install -r test-requirements.txt"
+  - "python setup.py install"
   - "pip install coveralls"
 script:
   - "python manage.py test"
-  - "python setup.py install"
   - "python setup.py build_sphinx"
 after_success:
   coveralls