modify pipx disclaimer of library installation --> include pipx inject <existing venv> <library> as an option

[iconoclasthero]

$ pipx install lyrics-in-terminal python-mpd2
  installed package lyrics-in-terminal 1.5.0, installed using Python 3.12.3
  These apps are now globally available
    - lyrics
done! ✨ 🌟 ✨

No apps associated with package python-mpd2 or its dependencies. If you are attempting to install a library, pipx should not be used. Consider using pip or a similar tool instead.

Admittedly, this is a poor example because the first comment is going to be that the lyrics-in-terminal[mpd] package exists to take care of my example, but that is not at all the point.

Let's say that you have a similar application that does not have an optional library packaged with it. Or, let's say that you installed lyrics and want to add python-mpd2 after the fact without reinstalling the base application (on the git, it says "For MPD player support install python-mpd2 package as well." Further, let's also assume that you use pipx rather infrequently irattically (e.g.,< 1x/quarter)... (or whatever, point is you have an existing pipx venv and you want a library in there so it'll work right.)

What would have dramatically reduced my frustration about this, now that I know that pipx can handle the installation** of e.g., lyrics-in-terminal in the first place ,would be to have a message that, instead of disclaiming the installation of libraries mentioned that "If you are attempting to install a library: pipx cannot be used to install system-wide libraries but additional or optional libraries needed for existing pipx-managed packages can be easily "injected" into the pipx venv using `$ pipx inject [], please see https://github.com/pypa/pipx?tab=readme-ov-file#inject-a-package and the documentation for more details."

I'm fairly sure that when I go to use pipx again in a few months, it will be a very helpful reminder that, oh, yes, pipx can actually solve my problem, right here, right now, with almost no fuss or hastle, exactly what I want. I don't need to mess around with pip or another tool I can just move on with one additional pipx call. It is difficult to express in words how useful it would have been to learn of the possibility from a cli message like the one that originally learned me about pipx. (**i.e. "If you wish to install a non-Debian packaged Python application, it may be easiest to use pipx install xyz, which will manage a virtual environment for you.")

$ pipx install lyrics-in-terminal --force; pipx install python-mpd2; pipx inject lyrics-in-terminal python-mpd2 --force
--python is ignored when --force is passed. If you want to reinstall lyrics-in-terminal with /usr/bin/python3, run `pipx reinstall lyrics-in-terminal --python /usr/bin/python3` instead.
Installing to existing venv 'lyrics-in-terminal'
  installed package lyrics-in-terminal 1.5.0, installed using Python 3.12.3
  These apps are now globally available, environment available to pipx
    - lyrics
done! ✨ 🌟 ✨
No apps associated with package python-mpd2 or its dependencies. If you are attempting to install a system-wide library, pipx should not be used; consider using pip or a similar tool instead.  Use `pipx inject <pipx venv> <package>` to install libraries, additional applications in pipx-managed venv.
  injected package python-mpd2 into venv lyrics-in-terminal
done! ✨ 🌟 ✨

[chrysle]

Thanks for the suggestion! This sounds indeed as if it might improve user experience. Besides, there's also the --preinstall option to pipx install that could be mentioned.