Updated README some more regarding paths
Updated README some more regarding paths

- Specify exact path to virtualenv since updating the PATH happens later
- Give download location for optional library, and describe the problems
  with pip a little better
- Fixed PYTHONPATH in pyhadoop so that imports between scripts actually
  work. Describe pyhadoop workings and give examples about making
  archives available on the worker nodes.

timvandermeij/sentiment-analysis,timvandermeij/sentiment-analysis