Please document use of sign-up plugin

Hi! I am trying to understand how to use the plugin. It is enabled (DMX 5.1, latest plugin release), I am logged in as admin. Self-registration is turned off. I want to create a user account with an e-mail address to use the "forgot password" functionality. I was expecting to be able

• to add the e-mail address either right underneath the user's password
• or to edit the account later which the admin doesn't have to permission to do
• or to create an e-mail address instance and link it to the account but there is no such topic type.

How do I add it? Could you please add this to the README file?