Updated snippet for "pan + rotation page"

[Davoodeh]

Hello,

I just noticed this page (https://bevy-cheatbook.github.io/cookbook/pan-orbit-camera.html) which comes pretty up high whenever Googled.

Since the page is for version 0.9 and in need of an update, I wanted to point out that there is this pretty helpful code to study instead, in the Bevy's current version repository which does basically the same thing and I think it needs to be mentioned on that page: bevy@examples/helpers/camera_controller.rs

Thank you for your awesome community and book! Keep up the good work.