Document why virtual environments should (nearly) always be used, and system site-packages is considered harmful

Every time someone comes here with something going wrong after they set poetry config virtualenvs.create false the answer is "oh, you didn't want to do that". It's a footgun.

Can anything be done?

• update the docs with more cautions?
• make that option harder to use / print a big old warning when it is used?
• add a new option with meaning "I really do want to use the system environment and acknowledge that it's probably a bad idea"
• other ideas?

Personally I don't want poetry to manage my virtual environments at all, though I do want it to refuse to go ahead if I've forgotten to create the environment myself. But probably it's hard to get to there from here; and certainly not everyone has the same workflow.

No files, tests, or entry points are named. Start by reviewing the documentation for poetry config virtualenvs.create and the existing discussion, then determine whether the scope is documentation, a warning, or a new configuration behavior. Done requires a decided approach that clearly explains system site-packages risks and reflects that decision in the project.