Mention some of the motivation for this package

Try to preemptively answer hypothetical questions like Why can't I just

```
    class Proxy(object):
        def __init__(self, obj):
            self.__obj = obj
        def __getattr__(self, a):
            return getattr(self.__obj, a)
        def __setattr__(self, a, v):
            setattr(self.__obj, a, v)
```