message: heading system props docs
diff: # Heading
  +## Default example
  ```.jsx
  <Heading fontSize={1} mb={2}>With fontSize={1}</Heading>
  -<Heading fontSize={2} mb={2}>With fontSize={2}</Heading>
  -<Heading fontSize={3} mb={2}>With fontSize={3}</Heading>
  ```
  +## System props
  +
  +Dropdown components get `TYPOGRAPHY` and 'COMMON' system props. Read our [System Props](/system-props) doc page for a full list of available props.
  +
  export const meta = {displayName: 'Heading'}
  