[email protected]: tweak EXTERNALLY-MANAGED guidance

Formula/p/python@3.12.rb

@@ -394,13 +394,29 @@ def post_install
  xyz, where xyz is the package you are trying to
  install.
 
- If you wish to install a non-brew-packaged Python package,
- create a virtual environment using python3 -m venv path/to/venv.
- Then use path/to/venv/bin/python and path/to/venv/bin/pip.
+ If you wish to install a Python library that isn't in Homebrew,
+ use a virtual environment:
 
- If you wish to install a non-brew packaged Python application,
- it may be easiest to use pipx install xyz, which will manage a
- virtual environment for you. Make sure you have pipx installed.
+ python -m venv path/to/venv
+ source env/bin/activate
+ python -m pip install xyz
+
+ If you wish to install a Python application that isn't in Homebrew,
+ it may be easiest to use 'pipx install xyz', which will manage a
+ virtual environment for you. You can install pipx with
+
+ brew install pipx
+
+ You may restore the old behavior of pip by passing
+ the '--break-system-packages' flag to pip, or by adding
+ 'break-system-packages = true' to your pip.conf file. The latter
+ will permanently disable this error.
+
+ If you disable this error, we STRONGLY recommend that you additionally
+ pass the '--user' flag to pip, or set 'user = true' in your pip.conf
+ file. Failure to do this can result in a broken Homebrew installation.
+
+ Read more about this behavior here: <https://peps.python.org/pep-0668/>
  EOS
  end
 
@@ -515,7 +531,7 @@ def caveats
  system bin/"pip#{version.major_minor}", "list", "--format=columns"
 
  # Check our externally managed marker
- assert_match "If you wish to install a non-brew-packaged",
+ assert_match "If you wish to install a Python library",
  shell_output("#{python3} -m pip install pip 2>&1", 1)
  end
 end