Restore notification footer text

As requested by @sytses in https://gitlab.com/gitlab-org/gitlab-ce/issues/1366#note_2317785:

We have problems with our email being marked as SPAM. I expect every automated email to inform me why > I'm receiving it. Some people might not have used GitLab for 2 years or their account might be automatically created.

I think we should have a message, but it should be generic enough so that it works in every case.

"You receive this email because of you account on HOSTNAME. To receive less emails please adjust your notification settings."

@ JobV Moving this to 8.1 since we should not ship without a message.