added entry on redirect after logout

[pigeonflight]

This pull request documents the process of customizing the logout functionality in Volto to automatically redirect users to the login page after they log out. By default, Volto does not redirect users to the login page after logging out, which can be confusing for users who expect to be taken back to the login page.

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📚 Documentation preview 📚: https://volto--6086.org.readthedocs.build/