Adding some resources to the book

[ghost]

Hi,
I just started graphics programming, and this is my first book. I found that it lacks explaination about viewport/canvas etc, which is quite important. I started reading it (writing code alongside, then I found myself lost, because the book doesn't explain stuff in depth (as much I expected as a beginner).
Then I found

• https://gabrielgambetta.com/computer-graphics-from-scratch/02-basic-raytracing.html
• https://gabrielgambetta.com/computer-graphics-from-scratch/A0-linear-algebra.html
  and those were quite helpfull. Can you please add these to the start of book so that others can take advantage of the free resource as well :)