DOC: update README with specific instructions

Add specific install and usage instructions.  Thanks to Ian Bell for the
report.  Closes gh-2.
DOC: reminder to import setuptools in setup.py

Thanks to Ian Bell for help debugging this one.
Merge pull request #4 from matthew-brett/update-docs

DOC: update README with specific instructions

Add specific install and usage instructions. Thanks to Ian Bell for the
report. Closes gh-2.