dokumentation enhancement for zone-cleaning-function
I have an enhancement for zone-cleaning:

You can use the miio-api in the terminal to test the coordinates for zone cleaning. You can drive manually to the coordinates by using `mirobo --ip [robo-ip] --token [robo-token] goto X_COORD Y_COORD`

It would be the easiest and quickest way to check the botton-left and top-right position of the zone in the real environment.

Additional hint:
- the position near the docking station is `25500 25500` (X/Y)
- Driving downwards the map is possible by decreasing X (i.e. `25000`)
- Driving upwards the map is possible by increasing X (i.e. `26000`)
- Driving left of the map is possible by decreasing Y (i.e. `25000`)
- Driving right the map is possible by increasing Y (i.e. `26000`)

For example a valid zone in the bottom-right map could be i.e. `27300 21000` (bottom left) `30300 23800` (top right)

![IMG_7500](https://user-images.githubusercontent.com/22019133/125193591-72b8b980-e24d-11eb-9867-f304524b894a.jpg)

