[i3] Fedora 34 i3 Spin Guide

I wrote a draft introduction to the i3 spin. Please review/edit it at https://hackmd.io/@kcwitt/ByvfH-QeY. It is pretty rough, but I wanted to put it out there to see what other things anybody thinks should be included. For example, I didn't include anything about changing the background image (because I never changed it myself since you don't see it much in a tiling window manager). Once all the issues have been identified and included, it probably needs a top down re-organization. Cheers, Casey