Added maximum_speed to vehicles

Author: schnuerle

data-types.md

@@ -33,6 +33,7 @@ A vehicle record is as follows:
 | `accessibility_options` | Enum[] | Required             | **[Mode](/modes#list-of-supported-modes) Specific**. [Accessibility options](/modes#accessibility-options) given as an array of enumerated values. List of any accessibility options **available on the vehicle**. |
 | `battery_capacity`   | Integer  | Required if Available | Capacity of battery expressed as milliamp hours (mAh) |
 | `fuel_capacity`      | Integer  | Required if Available | Capacity of fuel tank (liquid, solid, gaseous) expressed in liters |
+| `maximum_speed`      | Integer  | Required if Available | Maximum speed (kph) possible with vehicle under normal, flat incline, smooth surface conditions. Applicable if the device has a built-in or intelligent speed limiter/governor. |
 
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