handbook: use userid example other than `toor`

[emaste]

Summary

The toor account may be removed in the future. The example pw lock invocation does not need to reference a superuser account, so just use a hypothetical user's userid.

Sponsored by: The FreeBSD Foundation

[emaste]

change both toor examples

[emaste]

As for why imani, I wanted a generic example userid and just chose an arbitrary name from https://en.wikipedia.org/wiki/Unisex_name

[debdrup]

Putting aside the debate over the toor user for another time, using it as an example user doesn't seem like the best option, as it's meant to rescue systems.

I think it makes sense, and the change (what little of it there is) looks like good to me.