Add pipx installation instructions

[OpenBagTwo]

GIVEN Steve wants to install gsb on his system

WHEN he goes to the installation instructions page

THEN the recommended instructions should be to install gsb via pipx

SO that he doesn't have to worry about managing virtual environments

Notes

Note that gsb requires Python 3.11 or newer, and a lot (most?) systems still ship with Python 3.10 or older. A quick audit of my Linux boxes has the system Python as:

• Ubuntu 22.04: Python 3.10.12
• elementary OS 7.1: Python 3.10.12 (makes sense--it's based on 22.04)
• DietPi v8.21.1 / Debian GNU/Linux 12 (bookworm) (dietPi): 3.11.2
• SteamOS 3.4.10: 3.10.8 😬
• macOS 12.4: Python 3.8.9 🤣

(with my Arch machines waiting for a non-AUR 3.12 package)

So with that specified, the installation guide should be structured as a flowchart:

1. Open a terminal.
2. Run the command python3 -V
   • If you get 3.11 or later, install and use pipx
   • If you get 3.10 or older, use conda
   • If your terminal tells you that Python isn't installed on your system, install 3.11 or later using brew, conda or whatever