Document & hint that react and react-dom are already aliased to compat modules for Preact and Inferno app projects

[insin]

See #246

• This is currently only documented in the Quick Development guide.

  We've munged app-specific config into the documentation for nwb serve and nwb build generic commands (which are no longer used as part of project skeletons, so you can delete the default nwb.config.js file if you want). That's not ideal, but it's probably the right place to add this documentation for now.

• More visibly - check if the user has aliased react or react-dom in their preact/inferno app config and add a hint that they don't need to do this.

  Example of an existing hint.