Add note about not logging out of Element

docs/admin/10_configuration.rst

@@ -13,6 +13,9 @@ open the settings via ``Profile picture → All Settings``.
 Go to the tab ``Help & About`` and expand ``Access Token`` in the ``Advanced`` section.
 The access token will be displayed and can be copied.
 
+After that, do not log out of Element, because that would invalidate the access token.
+You might want to use a private tab in your browser or clear session data afterwards.
+
 Creating a new user via open registration
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