Address the python3 command issue on Windows

A lot of the support requests on pypa/packaging-problems are Windows users not being able to run the python3 command, since it is not shipped with the official CPython distribution. (recent example: pypa/packaging-problems#373)

Microsoft recently added a python3.exe stub that automatically opens the Windows Store page if you does not have the Store-provided Python installed. The problem is, the stub would silently do nothing if you pass any arguments to it, making users very confused.

I don’t have a perfect solution, unfortunately. The default python on macOS is still Python 2 (with a warning message), so that won’t work. py -3 is the recommended command for the official CPython distribution on Windows, but IIRC it is not shipped with the Windows Store distribution. The situation is quite bad, if I am being honest.

Comienza revisando el texto del issue y el ejemplo enlazado pypa/packaging-problems#373; después, compara el comportamiento de los comandos de CPython oficial y Microsoft Store descrito aquí. Define una recomendación concreta para los usuarios de Windows y documenta cómo gestionar los argumentos de python3; se considerará terminado cuando la guía aborde la confusión indicada sin depender de una elección de comando sin resolver.