Make compatible with pipx?

[ehmatthes]

I'm not too familiar with pipx, but I like how it describes a use case as "turning PyPI into an App Store for python".

• See if I can use pipx to install this project with an easier CLI entry point than the current implementation. (It shouldn't change current workflows, just make it easier for people who use pipx?)
• Add a note to documentation installation section that pipx can be used for system-wide installation.
• Also sort out how to install with uv. See reddit conversation: "uv lets you uv tool install python-based tools into dedicated venvs, at the user-level. It manages the venv for you. It keeps that tools reps isolated. It lets you just snag it and run it." Look at [uvx]](https://docs.astral.sh/uv/guides/tools/).

[ehmatthes]

This works, as of 8/1/2025:

$ pipx install py-image-border
  installed package py-image-border 2023.4.14.2, installed using Python 3.13.5
  These apps are now globally available
    - add-border
done! ✨ 🌟 ✨

I was able to use it as a CLI tool:

$ add-border status_python_versions.png 
New image saved at status_python_versions_bordered.png