docs: Neato D4 working (#197)

Added `Neato D4` to the list of supported models and this is what I see on attribute list:
```json
battery_level: 55
battery_icon: 'mdi:battery-charging-60'
status: Charging
clean_start: '2021-03-22 10:00:03'
clean_stop: '2021-03-22 10:47:04'
clean_area: 46.1856
clean_suspension_count: 0
clean_suspension_time: 0
clean_pause_time: 0
clean_error_time: 0
battery_level_at_clean_start: 96
battery_level_at_clean_end: 33
launched_from: schedule
friendly_name: Alfred
icon: 'mdi:robot-vacuum-variant'
supported_features: 15964
```

README.md

@@ -197,6 +197,7 @@ If this card works with your vacuum cleaner, please open a PR and your model to
 - Dyson 360 Eye
 - Neato D7
 - Neato D6
+- Neato D4
 - Shark IQ
 - Ecovacs Deebot 950
 - EcoVacs Deebot OZMO T8 AIVI