Update readme.md

Author: liminchen

readme.md

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 A curated collection of Python examples focused on optimization-based solid simulation with guarantees on algorithmic convergence, penetration-free and inversion-free conditions. The examples are designed for ease of readability and understanding.
 
 Introductory sections (with * following the titles) for each of the examples in this repository can be found in the free online book [Physics-based Simulation](https://phys-sim-book.github.io/).
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+A [MUDA](https://github.com/MuGdxy/muda)-based GPU version of the tutorial can be found at [solid-sim-tutorial-gpu](https://github.com/phys-sim-book/solid-sim-tutorial-gpu).