This is wrist mounted version of the Touch Pi by Adafruit. There is no major changes made from the original. I've only added a wrist mount for it. Including a spot for straps. The base needs to be printed with support.
You will need to change the orientation of the screen depending on which arm you want to wear it on. You may want to add come holes in the bottom for easier SD card and USB peripheral removal. Otherwise just follow the instructions given by Adafruit.
Raspberry Pi A+
Adafruit PiTFT 3.5"
2500mAh Lithium polymer battery
2 8" Straps
Full Tutorial: https://learn.adafruit.com/touch-pi-portable-raspberry-pi/