message: add component props docs for DonutChart
diff: DonutChart components get `space` system props. Read our [System Props](/system-props) doc page for a full list of available props.
  +## Component props
  +
  +| Prop name | Type | Description |
  +| :- | :- | :- |
  +| data | Object | Use the keys `error`, `pending`, and `success` to set values used to generate slices in the chart |
  +| size | Number | Used to set the width and height of the component
  +
  export const meta = {displayName: 'DonutChart'}
  