Update boot2docker docs with tls workaround

Is this is an appropriate solution to tls with boot2docker failing on OSX?

```python
from docker.client import Client
from docker.utils import kwargs_from_env

kwargs = kwargs_from_env()
kwargs['tls'].assert_hostname = False

client = Client(**kwargs)
print client.version()
```

Updating docs (also mentioned in https://github.com/docker/docker-py/issues/369#issuecomment-62772509)