Book 3 listing 38 (in section 12.2) doesn't tell the user how to handle the new `lights` parameter in `ray_color()`

[define-private-public]

https://raytracing.github.io/books/RayTracingTheRestOfYourLife.html#cleaninguppdfmanagement./handlingspecular

When I ran the code, I was getting some segfaults, then I realized that lights wasn't populated. This section should instruct the user how to collect the lights from listing 38 and then pass that into ray_color().

[hollasch]

• section 12.2

[hollasch]

Thanks!