Add base help for preview command
Add base help for preview command

NativeScript/nativescript-cli,NathanaelA/nativescript-cli,NativeScript/nativescript-cli,NathanaelA/nativescript-cli,NativeScript/nativescript-cli,NativeScript/nativescript-cli,NathanaelA/nativescript-cli,NathanaelA/nativescript-cli