Cannot setup mqtt_basic_async

Steps to reproduce.

- Clone repo
- Move *example-custom-config/custom_components/mqtt_basic_async* to *custom_components*
- Restart HA
- Add below to configuration.yaml

```
mqtt_basic_async:
topic: "home-assistant/mqtt_example"
```

- Go to Developer Tools and click check configuration to get:
```
Invalid config for [mqtt_basic_async]: [default_config] is an invalid option for [mqtt_basic_async]. Check: mqtt_basic_async->default_config. (See /config/configuration.yaml, line 29).
```

which is the 1st line in my configuration.yaml file.

Any ideas? I want to listen to some topics and update some sensors, already have these in sensors.yaml and they work fine, but I would like to develop a more complex integration, and this would be my 1st step :D