New tutorials: write section to define and describe "package"

(For more information about this issue, please see #194).

We need a short section to follow the prerequisites section (see #196) (i.e., as its own file). It should satisfy the following goals:

• explain what a distribution package is
• explain how a distribution package differs from import packages and modules
• use the terminology that the wider Python Packaging User Guide uses, so the terminology is familiar if the reader turns to another part of the guide

I also think it would be helpful if the section could illustrate each point with some kind of example, either a made-up example or a real-world example, if it's not too complicated.

When opening pull requests for this issue, please submit to the develop branch. If you have questions that concern contributing more generally, please use issue #194. Otherwise, feel free to comment with questions or feedback. Thanks!

Comienza revisando la sección de requisitos previos mencionada en el issue y las entradas enlazadas del glosario de Python Packaging User Guide sobre distribution packages, import packages y modules. El trabajo estará completo cuando un archivo de sección independiente siga a los requisitos previos, utilice la terminología de la guía e incluya ejemplos claros que distingan cada concepto; envía los cambios a la develop branch.