Update Readme.md to make python versions current

Would it be possible/useful to upgrade the default distribute, pip, and python that this buildpack uses?

distribute-0.7.3
pip-1.5.4
python-2.7.6
python-3.4.0
pypy-2.2.1

This buildpack successfully builds both python-2.7.6 and python-3.4.0 on IBM BlueMix.