Write release notes for occlusion culling

[alice-i-cecile]

@JMS55 mentioned that they thought this was worth calling out seperately from the other rendering perf improvements, and I agree! This is an optimization that makes sense to non-rendering experts and is relatively high impact for some users.

bevyengine/bevy#17934 handles this for deferred, but apparently another PR (bevyengine/bevy#17413) did it already for non-deferred. bevyengine/bevy#12898 did this for meshlets.

bevyengine/bevy#12889 was precursor work that might have useful context.

[JMS55]

Virtual geometry has actually had occlusion culling for even longer, iirc since the first PR :)

Also it's a little buggy, non-power-of-2 viewport sizes will be a little bugged. I can't remember if we made occlusion culling turned on by default or not for the normal rendering path because of this.

I've been meaning to fix this, but forgot...