chapters/compute/lecture-demos: Add `README.md`s to explain the demos

[teodutu]

#74 transitioned the Compute chapter to the Open Education Hub methodology, creating the lecture-demos subchapter [1]. These demos do not explain how to use them, what to observe, and what to learn from them.

Each demo requires a README.md file that should explain how to build and run it, as well as what to notice when running said demo.

[1] https://github.com/cs-pub-ro/operating-systems/tree/bce2316283a7585b23f9adfc54c85c89e3ed32cd/chapters/compute/lecture-demos