Include an example of pyproject.toml

Thanks for putting `pycowsay` together!

One thing I was missing quite a bit was what would the alternative/similar `pyproject.toml` look like. In particular, it seems many examples of `pyproject.toml` use `scripts` which are different from `entry_points` which [pipx expects](https://pypa.github.io/pipx/how-pipx-works/#developing-for-pipx).

Thanks again!

Start by reviewing the repository's existing documentation and the linked pipx guidance, then determine where a pyproject.toml example belongs. Add an example that shows the entry_points form pipx expects and explains how it differs from scripts; done when readers can compare the two approaches directly.

Written by the indexing model from the issue text.