message: update getting started doco; xref 551
diff: @@ -26,10 +26,12 @@ You can now view example-app in the browser.
  Run the following commands if you have Docker environment
  ```bash
  -$ docker build . -t spotify/backstage
  +$ yarn docker-build
  $ docker run --rm -it -p 80:80 spotify/backstage
  ```
  +> See [package.json](package.json) for other yarn commands/options.
  +
  Then open http://localhost/ on your browser.
  [Back to Docs](README.md)
  