fix package by explicitly including the README.md file

Should fix this:

```
~/.virtualenvs/1d842084af2761d2$ pip install csvgroup
Downloading/unpacking csvgroup
  Downloading csvgroup-0.1.tar.gz
  Running setup.py egg_info for package csvgroup
    Traceback (most recent call last):
      File "<string>", line 16, in <module>
      File "/home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup/setup.py", line 15, in <module>
        long_description=read('README.md'),
      File "/home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup/setup.py", line 8, in read
        return open(os.path.join(os.path.dirname(__file__), fname)).read()
    IOError: [Errno 2] No such file or directory: '/home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup/README.md'
    Complete output from command python setup.py egg_info:
    Traceback (most recent call last):

  File "<string>", line 16, in <module>

  File "/home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup/setup.py", line 15, in <module>

    long_description=read('README.md'),

  File "/home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup/setup.py", line 8, in read

    return open(os.path.join(os.path.dirname(__file__), fname)).read()

IOError: [Errno 2] No such file or directory: '/home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup/README.md'

----------------------------------------
Command python setup.py egg_info failed with error code 1 in /home/kr/.virtualenvs/1d842084af2761d2/build/csvgroup
```

See also [specifying the files to distribute](http://docs.python.org/2/distutils/sourcedist.html#specifying-the-files-to-distribute)