include .rst so package can install

Otherwise you get this on install:

```
    with open(os.path.join(here, 'CHANGES.rst')) as f:

IOError: [Errno 2] No such file or directory: '/private/var/folders/h5/cbsbsk_j0f984db_n771zwz00000gn/T/pip_build_andy/monolith.aggregator/CHANGES.rst'
```