[Docs] Add guide for development VM setup

[rainestorme]

Sometimes it's not feasible to test on actual hardware, and QEMU with a TPM emulator can run ChromeOS with fake-dmserver, as shown in r58's post. I've used this method in the past to test a few changes, but there is no consistent method of setting it up. This might be worthy of a completely seperate project, but at the very least a rough outline of how to accomplish it would be useful.