Improve README

[PeterNerlich]

Clean up the README so new people quickly find their way around. Split into more files linked to from the README if necessary (e.g. INSTALL for detailed build/installation instructions).

My biggest complain with the current version:
I have no idea what this project is actually about. User story: I am searching for a way to generate tracking data from a webcam face tracker to feed into Steam VR as if there was a true VR tracking setup present. In this moment it is unclear to me whether this is a dummy driver that allows me to do this, only allows other systems to work with Steam or maybe something completely different, just for displaying a VR video stream on such displays, as I am not (yet) familiar with the abbreviation "HMD" (best guess: Heads Mmm.... uh, Display).

I think it would be nice if the first paragraph below the project title was a one or two sentence description of what this project is meant to address.

[dtruesdale88]

This is for VR HMD's (Head Mounted Display). The open driver OpenHMD works with SteamVR supporting specific HMD's. This specific project is about taking the OpenHMD driver and installing it into SteamVR to allow the list of VR Devices to work in Linux using SteamVR.