message: tweak Button docs
diff: `Button` is used for actions, like in forms, while `Link` is used for destinations, or moving from one page to another.
  -In special cases where you'd like to use an `<a>` styled like a Button, use `<Button is='a'> and provide an `href`.
  +In special cases where you'd like to use a `<a>` styled like a Button, use `<Button is='a'>` and provide a `href`.
  ## Default examples
  