Add a basic README

README.md

+A tiny script which uses Rust's NVML wrapper to tweak some parameters for NVIDIA GPUs.
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+It requires to be ran as root. [See NVML API Reference Guide](https://docs.nvidia.com/deploy/nvml-api/group__nvmlDeviceCommands.html).
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+For now, it handles the following parameters :
+- [Power limit](https://docs.nvidia.com/deploy/nvml-api/group__nvmlDeviceCommands.html#group__nvmlDeviceCommands_1gb35472a72da70c8c8e9c9b108b3640b5)
+- [Clock offset](https://docs.nvidia.com/deploy/nvml-api/group__nvmlDeviceCommands.html#group__nvmlDeviceCommands_1g09cbcfd131202a31e94f83c30566d5cd)
+- [Memory clock offset](https://docs.nvidia.com/deploy/nvml-api/group__nvmlDeviceCommands.html#group__nvmlDeviceCommands_1g59520f6bf90eaaa2e700a9ba518c79ca)