feat: add README.md for the samples/ subdirectory

Author: madhav-madhusoodanan

samples/README.md

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+# Rust-Cuda Samples
+
+These are the Rust-Cuda port of the samples from Nvidia's [cuda-samples](https://github.com/NVIDIA/cuda-samples/tree/master/Samples) repository.
+
+1. Chapter 0: [Introduction](https://github.com/Rust-GPU/rust-cuda/samples/introduction)

samples/introduction/README.md

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+# Chapter 0: Introduction
+
+## [asyncAPI](https://github.com/Rust-GPU/rust-cuda/samples/introduction/async_api)
+This example demonstrates two key capabilities of CUDA events: measuring GPU execution time and enabling concurrent CPU-GPU operations.
+
+1. Events are recorded at specific points within a CUDA stream to mark the beginning and end of GPU operations.
+2. Because CUDA stream operations execute asynchronously, the CPU remains free to perform other work while the GPU processes tasks (including memory transfers between host and device)
+3. The CPU can query these events to check whether the GPU has finished its work, allowing for coordination between the two processors without blocking the CPU.