Make the installation scripts install Node and tns

Currently our recommended quick installation is a three-step process: install Node, install tns, and then run our setup scripts. Even though those steps are relatively minimal, a surprising number of people get tripped up going through them. See https://github.com/NativeScript/docs/pull/585 for an example.

I want to propose that we change the installation scripts to install everything—Node, tns, and the various system requirements. The scripts could detect whether Node is installed, as to avoid undoing a user’s installation unknowingly.

A single script would simplify the documentation considerably, but it would probably be a non-trivial engineering effort. And with installers in the works perhaps this isn’t worth the effort. But I wanted to open this up to see what people think.

Thoughts?

Como el issue no nombra archivos, pruebas ni puntos de entrada, comienza localizando los scripts de instalación y la documentación de configuración rápida. Un cambio completado haría que los scripts instalaran Node, tns y los requisitos del sistema, detectando al mismo tiempo una instalación existente de Node, y que la documentación se redujera a un flujo de configuración más sencillo.