Comment 2 for bug 1577528

It's part of bash.

debian/etc.bash.bashrc contains this section.

# sudo hint
if [ ! -e "$HOME/.sudo_as_admin_successful" ] && [ ! -e "$HOME/.hushlogin" ] ; then
    case " $(groups) " in *\ admin\ *|*\ sudo\ *)
    if [ -x /usr/bin/sudo ]; then
 cat <<-EOF
 To run a command as administrator (user "root"), use "sudo <command>".
 See "man sudo_root" for details.

 EOF
    fi
    esac
fi