Missing info in https://doc.babylonjs.com/how_to/webxr_session_manage.

[ankitcsr]

sessionManager.initializeAsync should be called before sessionManager.initializeSessionAsync .XR not defined error will pop up if initializeAsync is not called before initializeSession .Currently initializeAsync is not mentioned in the docs

https://doc.babylonjs.com/how_to/webxr_session_manager#basic-usage-and-initialization
https://playground.babylonjs.com/#MGH3JX