Since he was going to be carrying his Kindle anyway, ponnuki wanted to find a way to add a useable keyboard so he could use the K3 as a Linux box. It turned out that the easiest way to do that was to add a Raspberry pi as the hub. Like most ereaders, the Kindle isn't set up for USB Host, which is what you would need for the K3 to recognize that you'd plugged in a keyboard.
Ponnuki has posted an extensive set of instructions,but the short-short version is that this project requires hacking a Kindle and programming the Raspberry Pi, both of which are moderately complicated technical problems. But once you get past them you'll end up with this:
All in all this is a cool project, but if I were inclined to do it I'd stop at just hacking the K3. It already has a keyboard, and while I don't like it much the built in keyboard still outweighs hassle of plugging in an external keyboard.
But if you do try this project, please do me the favor of playing Doom on your new Linux box. Don't forget to share some screenshots.