Update "using new templates" wiki page 

After we have clearer, "official" getting started steps for the new arch templates, (see https://github.com/microsoft/react-native-windows-samples/issues/980) we want to make sure we update the [new arch wiki page](https://github.com/microsoft/react-native-windows/wiki/Using-the-new-architecture-templates) to point end users to the official docs and not our internal testing docs