HDR and sRGB Values in Bevy

[studnikoff]

While studying the Bevy engine and the 2D Bloom example, I noticed that the example compiles and works fine, but the documentation is unclear about handling large color values, especially with HDR.

A similar issue was raised over a year ago:

I guess at this point I would be happy if there was a small mention in the documentation that large values are allowed with HDR, and Mul implementation for Srgb and LinearRgb to manipulate HDR brightness (palette has this too).

All color space conversions may not work very well with HDR but maybe it doesn't matter if they weren't even designed for that.

Originally posted by @eero-lehtinen in #12089

I suggest updating the documentation to clarify how HDR works with large values.
#20281