Create README.md

Add benchmarks top-level README

Author: WuhanMonkey

tools/benchmarks/README.md

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+# Benchmarks
+
+* inference - a folder contains benchmark scripts that apply a throughput analysis for Llama models inference on various backends including on-prem, cloud and on-device.
+* llm_eval_harness - a folder contains a tool to evaluate fine-tuned Llama models including quantized models focusing on quality.