I'll never figure out why people post this kind of stuff here (and then it gets upvoted). there's literally nothing "hacker" related or even novel about these notes - it's just bog standard stochastic process. like these are just notes for some grad class or something. invariably someone will pop in and respond to my complaint saying "well actually I used everything in these notes for a project 10 years ago". ok. it strikes me, strongly, as just weird virtue signaling.
If you prefer short video lectures, Complexity Explorer also has a Random Walks tutorial: https://www.complexityexplorer.org/courses/46-random-walks
It's a bit more visual, but still gets quite math-y enough for my taste.