Write introduction to new packaging tutorials

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

To kick off the introductory tutorial to Python packaging, we need a short section that answers the questions Who is this tutorial for? and What will be covered in the tutorial?.

For the first question, that means Python users who are at at least an "advanced beginner" level. They should be comfortable importing something from the standard library and comfortable with using common language features (like loops and if statements). Readers who want to learn to program with Python should be directed elsewhere.

The remainder of the intro should briefly describe what the reader can expect to learn by completing the guide. See #194 for details.

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!

Read issue #194 first for the packaging tutorial details, then identify the introductory tutorial section that needs the new text. Write a short introduction covering the intended audience and what the guide teaches, and submit the pull request against the develop branch.