message: docs: add example of how to use custom colorScheme
diff: @@ -48,6 +48,11 @@ function Usage() {
  }
  ```
  +You can also use the color for the `colorScheme` prop like this:
  +```jsx live=false
  +<Button colorScheme="brand">Click me</Button>
  +```
  +
  > If you're curious as to what theme styles you can override, please reference
  > the
  > [default theme foundation style files](https://github.com/chakra-ui/chakra-ui/tree/master/packages/theme/src/foundations).
  