Kali Linux can be installed on a Raspberry Pi 2 and earlier models such as the A or B+.
To get Kali running on a Raspberry Pi we need to download the image file and then burn it to a media such as a micro SD card or flash drive.
If you have never flashed a image file before it is a easy task to do.
A image file is a operating system that is pre-setup and simply needs to be copied to a bootable media.
Since the hardware on a Raspberry Pi 2 is already known there is no need to compile a kernel install drivers and so on.
A image file saves you the trouble of doing all that an simply need to be written to a SD card/Flash drive.
Steps to Installing Kali Linux on the Raspberry Pi.
Download the correct Raspberry Pi image file from Kali Linux download section here. https://www.offensive-security.com/kali-linux-arm-images/
UPDATE: Kali has been updated to Kali 2.0. Some have had problems with Kali 2.0 so I have uploaded Kali 1.1 to 4shared which can be found here. http://www.4shared.com/file/U1-TTKK0ba/kali-110-rpi2img.html
Be sure to get the correct image for your model since there are image files for model A, B+, and the Raspberry Pi 2.
Download Win32 Disk imager here. http://sourceforge.net/projects/win32diskimager
Download 7-zip here.http://www.7-zip.org/
The image file will be in a .XZ file format that needs extracting. Most likely you don’t have the software to unzip a .XZ file.
Extract the Raspberry Pi Kali Linux image file.
Run Win32 disk imager and load the image file into it. Select the right drive the SD Card/flash drive is on and click write.
Insert the SD Card into the Raspberry Pi, power it up allowing Kali to boot and it will come up to a login screen.
The login is “root”
The password is “toor”
Type the command “startx” to run the GUI.
Here is a step by step video.