Add README.md with project description, features, and directory structure

Author: algotyrnt

README.md

@@ -0,0 +1,33 @@
+# cache0
+
+![Build Status](https://github.com/algotyrnt/cache0/actions/workflows/run_tests.yml/badge.svg)
+![Language](https://img.shields.io/badge/language-C++17-blue.svg)
+![License](https://img.shields.io/badge/license-MIT-green.svg)
+
+**cache0** is a lightweight, persistent Key-Value store built from scratch in C++. It is designed to demonstrate core systems programming concepts including memory management, file persistence (RAII), and the Standard Template Library (STL).
+
+## Features
+
+- **In-Memory Speed:** Uses `std::unordered_map` for $O(1)$ average time complexity on lookups.
+- **Persistence:** Automatically saves data to disk on exit and loads on startup (RAII pattern).
+- **Safety:** Utilizes `std::optional` to handle missing keys gracefully.
+- **Modern C++:** Written in C++17.
+
+## Getting Started
+
+### Prerequisites
+- A C++ compiler supporting C++17 (GCC, Clang, or MSVC).
+
+### Directory Structure
+```text
+Cache0/
+├── include/
+│   └── cache0.hpp      # The Product (Header-Only Library)
+├── src/
+│   └── main.cpp        # The Example/Demo file
+├── tests/
+│   └──test_cache0.cpp  # Unit Tests
+├── .gitignore          # The ignore file
+├── .github/            # The CI workflow
+└── README.md           # Readme File
+```