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!

Commencez par examiner la section des prérequis indiquée dans l’issue ainsi que les entrées du glossaire de Python Packaging User Guide consacrées aux distribution packages, import packages et modules, qui y sont liées. Le travail est terminé lorsqu’un fichier de section autonome suit les prérequis, utilise la terminologie du guide et contient des exemples clairs distinguant chaque concept ; soumettez les modifications à la develop branch.