message: docs: expand configuration usage
  Followup to
  PR Close
diff: @@ -174,6 +174,12 @@ By default, a `production` configuration is defined, and the `ng build` command
  You can define and name additional alternate configurations (such as `stage`, for instance) appropriate to your development process. Some examples of different build configurations are `stable`, `archive` and `next` used by AIO itself, and the individual locale-specific configurations required for building localized versions of an app. For details, see [Internationalization (i18n)](guide/i18n#merge-aot).
  +You can select an alternate configuration by passing its name to the `--configuration` command line flag.
  +
  +You can also pass in more than one configuration name as a comma-separated list. For example, to apply both `stage` and `fr` build configurations, use the command `ng build --configuration stage,fr`. In this case, the command parses the named configurations from left to right. If multiple configurations change the same setting, the last-set value is the final one.
  +
  +If the `--prod` command line flag is also used, it is applied first, and its settings can be overridden by any configurations specified via the `--configuration` flag.
  +
  {@a build-props}
  ### Additional build and test options
  