This is just a shout-out to my first guide attempt… The comments added by users on Instructables are very useful so it isn’t worth while copying over the same information to this site. Check out the video explaining the button here:
Since the Raspberry Pi foundation decided to leave out an off button to safely shutdown the Raspberry pi, I’ll show you a simple method I came up with to build one, so there are no more excuses for yanking the power cable out of your Pi!
This method uses no extra components apart from a piece of wire, so as long as you have a way of connecting two pins together you can get on and make this right away.
This instructable assumes you know the basics of using a Raspberry Pi, i.e. connecting it to a monitor and keyboard / SSH into it and being able to type commands into the terminal.
Soldering is also useful but not totally necessary to make a more useful button.