cd /etc/grub.d/
sudo nano 40_custom
#!/bin/sh
exec tail -n +3 $0
# This file provides an easy way to add custom menu entries. Simply type the
# menu entries you want to add after this comment. Be careful not to change
# the 'exec tail' line above.

menuentry "Windows 7" {
      set root='(hd0,1)' chainloader +1
}
sudo grub-mkconfig -o /boot/grub/grub.cfg
sudo reboot