Split "pipx install" setup command into two commands on the documentation site

[nomadmtb]

Change Summary

I was working through the contributing section on the docs site and I noticed that if you run the pipx install command exactly as described, it would fail since pipx can't install multiple packages in the same call. So I ended up breaking it into two pipx install commands.

This was a pretty minor change so I didn't create an issue, but I'm more than happy to if we want to discuss more things there.

I did run through the rest of the stuff on the contributing / setup instructions and everything else looked good. 😄

Thank you!

Before

$ pipx install pdm pre-commit
usage: pipx [-h] [--version]
            {install,uninject,inject,upgrade,upgrade-all,uninstall,uninstall-all,reinstall,reinstall-all,list,run,runpip,ensurepath,environment,completions} ...
pipx: error: unrecognized arguments: pre-commit

After

$ pipx install pdm
  installed package pdm 2.8.0, installed using Python 3.11.4
  These apps are now globally available
    - pdm
done! ✨ 🌟 ✨

$ pipx install pre-commit
  installed package pre-commit 3.3.3, installed using Python 3.11.4
  These apps are now globally available
    - pre-commit
done! ✨ 🌟 ✨

Checklist

• The pull request title is a good summary of the changes - it will be used in the changelog
• Unit tests for the changes exist
• Tests pass on CI
• Documentation reflects the changes where applicable
• My PR is ready to review, please add a comment including the phrase "please review" to assign reviewers

[hramezani]

Thanks @nomadmtb