Programmatic gradients documentation

Hi Freya, thanks for this great addition to Unity, it's been a pleasure to use so far.

One thing I'm stuck on though, is programmatically filling a Polygon with a linear gradient in ImmediateMode - it's not immediately obvious what objects and settings need to be applied, where.

Would you be able to provide a quick example of how to set this up? 

It might well be worth adding a bit about this (and maybe a little bit about the Polygon/line Bezier functions) to the documentation or samples as I've had to really dig to find info about how they work, and they're some of the most exciting parts of this package!

Many thanks

Tom