I don't think the command was documented somewhere. But maybe a simple note could be added in the "How to Manually Encode a Password" page for the cases someone is seeking how to manually encode the password, but does not search the programmatic way (for instance when adding a user to the in_memory provider)

Closing it as "won't fix" because we already mention the command here http://symfony.com/doc/current/security.html#c-encoding-the-user-s-password and we don't explain the details or show its output ... so there's nothing to update!