Add a basic setup.py (fixes #4)

This allows newsbuilder and its tests to be installed.

To test, install newsbuilder in a clean virtual env. eg
```
mkvirtualenv newsbuilder-setup-4
pip install --editable .
```

And then run the tests and the build-news command.

```
trial newsbuilder
newsbuilder ~/projects/Twisted/trunk
```

Fixes: #4 
Having fixed the README path, I find that I still can't install the package from outside the root.

It seems that setuptools searches recursively from the CWD which takes ages.

I can't find any information about changing that behaviour but this SO question seems to be related.
 * https://stackoverflow.com/questions/14865990/python-module-wont-install

The answer isn't really helpful though.

Here's where it appears to hang while it searches my entire projects directory. `lsof` shows it recursively opening every file!

```
(newsbuilder-setup-4)[~/projects]$ python Twisted/newsbuilder/setup.py install
running install
running bdist_egg
running egg_info
creating newsbuilder.egg-info
writing requirements to newsbuilder.egg-info/requires.txt
writing newsbuilder.egg-info/PKG-INFO
writing top-level names to newsbuilder.egg-info/top_level.txt
writing dependency_links to newsbuilder.egg-info/dependency_links.txt
writing manifest file 'newsbuilder.egg-info/SOURCES.txt'
^Cinterrupted
```

So I'll ignore this for now and merge. As I said before, `pip install` doesn't have any of these problems.