Not a reading guide, but Computerphile have a good introductory video on Gaussian Splats: https://youtu.be/VkIJbpdTujE?si=8hoMbMx6tKuMZo2S
Individualkex also has a couple videos on the high level ideas: https://youtu.be/GQXDjzNWuPc?si=zlAN7dO9STGATKad