Split Hardware Requirements into 3 types, updated Software to match

[ExileInParadise]

On the index page, I have added some notes about the (painful) way to work through the course using only a single Pi, as well as notes on using David Welch's Pi-to-Pi serial cable/bootloader05 method. To do this, I split the hardware requirements into 3 sections - one for minimal development using a single pi, sd card writer, and 2 sd cards... the Second PC development method which the course was designed around, and then the Pi-to-Pi method is suggested with links to David Welch's github for the details.

Also, I split the software section a little to explain that the Minimal and Pi-to-Pi development environment would use the binutils/gcc included with the Raspbian Linux used to do the development work, and that the Second PC development environment would require installing or building a cross-compiler toolchain.