Document MapView min/max zoom properties (react-native-maps#1538)

Author: codedre

docs/mapview.md

@@ -22,6 +22,8 @@
 | `showsIndoors` | `Boolean` | `true` | A Boolean indicating whether indoor maps should be enabled.
 | `showsIndoorLevelPicker` | `Boolean` | `false` | A Boolean indicating whether indoor level picker should be enabled. **Note:** Android only.
 | `zoomEnabled` | `Boolean` | `true` | If `false` the user won't be able to pinch/zoom the map.
+| `minZoomLevel` | `Number` | `0` | Minimum zoom value for the map, must be between 0 and 20
+| `maxZoomLevel` | `Number` | `20` | Maximum zoom value for the map, must be between 0 and 20
 | `rotateEnabled` | `Boolean` | `true` | If `false` the user won't be able to pinch/rotate the map.
 | `scrollEnabled` | `Boolean` | `true` | If `false` the user won't be able to change the map region being displayed.
 | `pitchEnabled` | `Boolean` | `true` | If `false` the user won't be able to adjust the camera’s pitch angle.