Explain how RegularPolygon mesh is generated

[stepancheg]

I didn't notice minus where vertices are generated, so could not understand the order there.

Adding a comment to help the next person who is going to understand Bevy by reading its code.

[Jondolf]

I'm working on mesh generation for primitives and have changed some things around, so this might get changed later if the new implementations get approved. Here for example, my implementation just adds the actual vertices in CCW order, so you don't need to reverse the indices.

Useful comment to have for now though, no objections against it

Edit: Accidentally said CW, meant the opposite haha