Added an OpenXR render models demo

xr/openxr_render_models/README.md

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+# OpenXR Render models demo
+
+This is a demo showing OpenXR's render models implementation.
+
+Language: GDScript
+
+Renderer: Compatibility
+
+> [!NOTE]
+>
+> This demo requires Godot 4.5 or later
+
+## Screenshots
+
+![Screenshot](screenshots/render_model_demo.png)
+
+## How does it work?
+
+OpenXR allows us to run our application without having knowledge of the hardware being used,
+or that we as developers have access too at the time of developing our application.
+
+As a result we don't have direct information telling us what hardware is being used,
+however there are situations where we want to visually show this hardware.
+
+This specifically applies to the controllers used by the user, as showing the correct hardware
+improves the user's sense of immersion.
+
+The render model API allows us to enumerate the devices currently in use and then query
+information such as its 3D asset, its position and orientation in space, and the position
+and orientation of individual components of the asset.
+
+Godot's implementation hides most of the complexity of this through the OpenXRRenderModelManager
+node as a child of the XROrigin3D node. You can add just this node by itself and let it show
+all render models that are currently active, or like we do in this demo, you can add nodes
+in the tree of each controller to show render models related to that controller.
+
+## Action map
+
+This demo project has a barebones action map as we're only dealing with positioning.
+
+## Running on PCVR
+
+This project can be run as normal for PCVR. Ensure that an OpenXR runtime has been installed.
+
+## Running on standalone VR
+
+You must install the Android build templates and OpenXR loader plugin and configure an export template for your device.
+Please follow [the instructions for deploying on Android in the manual](https://docs.godotengine.org/en/stable/tutorials/xr/deploying_to_android.html).
+
+