Editing activation email

Hi all,

I run a multisite network, and on one individual blog I would like to invite subscribers to visit my private posts. They can’t register for an account, it’s invitation only. When I add a user in the WordPress backend they get the following email:

Hi,
You’ve been invited to join ‘Lorem Ipsum’ at
http://loremipsum.com/nl with the role of subscriber.
If you do not want to join this site please ignore
this email. This invitation will expire in a few days.

Please click the following link to activate your user account:
http://loremipsum.com/nl/wp-activate.php?key=44b13cd248bc937a

I’d like to edit this email but I can’t find where to edit this, can someone point me in the right direction?

Thanks in advance,

Ja Lav