Windows 7 not in boot options under GRUB

Windows 7 not in boot options under GRUB

sudo fdisk -l in Kali Linux terminal prints:
Disk /dev/sda: 320.1 GB, 320072933376 bytes
255 heads, 63 sectors/track, 38913 cylinders, total 625142448 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x70c6ed08

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *      206848   204802047   102297600    7  HPFS/NTFS/exFAT
/dev/sda2       204802048   625139711   210168832    7  HPFS/NTFS/exFAT

Disk /dev/sdb: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders, total 976773168 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x000bb220

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1            2048   961060863   480529408   83  Linux
/dev/sdb2       961062910   976771071     7854081    5  Extended
/dev/sdb5       961062912   976771071     7854080   82  Linux swap / Solaris
I have just installed Kali Linux on my 5GB external hard disk. My Windows 7 system is in /dev/sda2 and /dev/sda1 is a backup partition.
The Windows 7 option does not appear during restart – I think it has something to with installing Kali Linux. It asked me to install "master boot" (not quite sure about that).
I need Windows 7 to be able to switch between Kali Linux and Windows 7.