Update recommendation on Python version

[carolbooth2]

The current recommendation in the 'setup' section is

"Regardless of how you choose to install it, please make sure you install Python version 3.x (e.g., 3.6 is fine)."

According to https://devguide.python.org/versions/ the current lowest security patched version is 3.9 so this should be updated to something like:

"Regardless of how you choose to install it, please make sure you install Python version 3.9 or higher (e.g., 3.11 is fine)."
or
"Regardless of how you choose to install it, for your security please make sure you install an in-support version of Python version 3. You can check supported versions at https://devguide.python.org/versions/"

[carolbooth2]

_includes/install_instructions/python.html