Rework "Installing the remaining GDK Tools & Resources" section

Overview

On prepare.md - Under Installing the remaining GDK Tools & resources, we should evaluate these against the individual install notes. Reorganizing this doc so that this section doesn't need to exist seems ideal.

Proposal (optional)

Each of these items is either a) duplicative of instructions in the OS-specific sections or b) not particularly useful. We should re-evaluate each of these items to ensure they're still needed and either remove them or merge them in to the specific sections.