message: docs: add to update instructions
  PR Close
diff: @@ -7,9 +7,13 @@ This guide contains everything you need to know about updating to the next Angul
  If your application uses the CLI, you can update to version 9 automatically with the help of the `ng update` script:
  ```
  -ng update @angular/cli @angular/core
  +ng update @angular/cli@next @angular/core@next
  ```
  +<div class="alert is-important">
  +During the RC period, the `@next` tag is required. This flag will no longer be necessary once version 9 final is released.
  +</div>
  +
  The script will run a series of small migrations that will transform the code of your application to be compatible with version 9.
  If you're curious about the specific migrations being run (e.g. what code is changing and why), see the [automated migrations section](#migrations).
  