Relax the requirement for opting-out of required venv

Author: pradyunsg

pep-0704.rst

@@ -40,7 +40,7 @@ Specification
 
 When a user runs an installer without an active virtual environment, the installer MUST print an error message and exit with a non-zero exit code. The error message MUST inform the user that a virtual environment is required, SHOULD provide shell-specific instructions on how to create and activate a virtual environment named ``.venv``, and SHOULD provide a link to a documentation page that explains how to create and activate a virtual environment.
 
-The installer MUST also provide an command line option to disable this behaviour, allowing a user to opt-in to running the tool outside of a virtual environment. The installer MAY include this in the error message that it prints, and MUST include it in the documentation page it links to.
+The installer SHOULD also provide a mechanism to disable this behaviour, allowing a user to opt-in to running the tool outside of a virtual environment. The installer MAY include this in the error message that it prints, and MUST include it in the documentation page it links to.
 
 If the installer includes a link to a documentation page in the error message described above, the documentation page SHOULD be written with a focus on new users. It should explain what virtual environments are, why they are required, and how to create and activate a virtual environment. It SHOULD include instructions for the most common shells and platforms.