message: docs: add TS code example for extendTheme with config
  * Update color-mode.mdx
  Add a typescript  explanation for changing the theme config in color mode page.
  * Update color-mode.mdx
  Replace 'theme.tsx' with 'theme.ts'
diff: @@ -49,6 +49,26 @@ const theme = extendTheme({ config })
  export default theme
  ```
  +For typescript, you need to explicitly describe the theme config type as `ThemeConfig` object.
  +
  +```jsx live=false
  +// theme.ts
  +
  +// 1. import `extendTheme` function
  +import { extendTheme, ThemeConfig } from "@chakra-ui/react"
  +
  +// 2. Add your color mode config
  +const config : ThemeConfig = {
  + initialColorMode: "light",
  + useSystemColorMode: false,
  +}
  +
  +// 3. extend the theme
  +const theme = extendTheme({ config })
  +
  +export default theme
  +```
  +
  > Remember to pass your custom `theme` to the `ChakraProvider`, otherwise your
  > color mode config won't be taken into consideration.
  