add README.md

Author: froghramar

README.md

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+Design Patterns Examples
+
+This solution demonstrates simple design pattern examples in C# targeting .NET 10 (C# 14).
+
+Projects
+- `DesignPatterns` - Console demo showing Factory and Singleton patterns.
+  - Factory implementation: `DesignPatterns/Factories`
+  - Singleton implementation: `DesignPatterns/Singleton/Logger.cs`
+- `Tests` - xUnit tests covering the factory and singleton examples.
+
+Requirements
+- .NET 10 SDK
+
+Common commands
+- Build solution: `dotnet build`
+- Run console demo: `dotnet run --project DesignPatterns`
+- Run tests: `dotnet test`
+
+Notes
+- The `Logger` singleton is thread-safe and uses `System.Lazy<T>` with a `ConcurrentQueue<string>` to store messages.
+- Tests are located in the `Tests` project; see `Tests/ShapeFactoryTests.cs` and `Tests/SingletonTests.cs`.