message: docs: add note about transition and keepalive
diff: })
  ```
  - The object returned in `scrollBehavior` is now similar to [`ScrollToOptions`](https://developer.mozilla.org/en-US/docs/Web/API/ScrollToOptions): `x` is renamed to `left` and `y` is renamed to `top`.
  +- `transition` and `keep-alive` must now be used **inside** of `RouterView` via the `v-slot` API:
  + ```vue
  + <router-view v-slot="{ Component }">
  + <transition>
  + <keep-alive>
  + <component :is="Component" />
  + </keep-alive>
  + </transition>
  + </router-view>
  + ```
  + See more on the [KeepAlive](https://github.com/vuejs/vue-router-next/blob/master/e2e/keep-alive/index.ts) and the [Transition](https://github.com/vuejs/vue-router-next/blob/master/e2e/transitions/index.ts) examples.
  ### Typings
  