Update README to describe:

• OpenVR vs OpenXR environmens
  • Update the terminology and API from "XR Runtime" to "XR Backend" #152
• The different OpenXR runtimes and explain that only can be active at a time, explain how a specific one can be enabled (either through the runtime specific software or using an external tool like openxr-explorer¹ (or xrsetenvironment)
• How to set up remote rendering using HoloLens (what to install, how to configure, how to start)²
• Introduce the concept of actions file and bindings and list the ones currently provided.

Related

• Refactoring to support OpenVR and OpenXR, and streamline reuse in SlicerMixedReality  #121 (comment)