Document Ionic CLI documentRoot setting

[philonor]

Feature Request

CLI version: 3.12.0

Description:
Setting a documentRoot in ionic.config.json lets ionic serve serve from that custom directory. This setting is not documented in https://ionicframework.com/docs/cli/configuring.html and should be documented.

[imhoffd]

Thanks @philonor! We're in the process of writing documentation for CLI v4. The documentRoot setting is only for Ionic 1. I'll be sure to include it in the docs.

[imhoffd]

I think this would be better in the output of ionic serve --help for Ionic 1 projects.