docs: add overview documentation for CSharpWasm

Documentation/CSharpWasm.md

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+# CSharpWasm Documentation
+
+## Purpose 
+
+CSharpWasm project enables users to execute C# code directly within their browser for SK Online (SKO).
+The system relies on .NET 8 WebAssembly and Roslyn to execute user-submitted C# code while providing SplashKit functions through JavaScript interop.
+
+The documentation provides essential information to help contributors understand the system architecture and build process and usage of the system.
+
+
+
+## Project Layout  
+
+The following shows the structure of the `CSharpWasm/`
+
+```
+CSharpWasm/
+├─ Properties/
+│  ├─ AssemblyInfo.cs           
+│  └─ launchSettings.json      
+├─ .gitignore                  
+├─ CSharpCodeRunner.cs        
+├─ CSharpWasm.csproj           
+├─ Program.cs                 
+├─ SplashKitBindings.Generated.cs 
+├─ buildAndCopy.sh             
+└─ runtimeconfig.template.json 
+```
+
+| File / Folder                    | Role              | Responsibilities                                                                           |
+| -------------------------------- | ----------------- | ------------------------------------------------------------------------------------------ |
+| `CSharpCodeRunner.cs`            | Compiler & Runner |The `CompileAndRun` function performs  main operations which include loading reference assemblies followed by Roslyn-based C# compilation and then running the `Main()` function when it exists.|
+| `SplashKitBindings.Generated.cs` | C# ↔ JS Interop   | The generated file contains `JSImport` bindings which expose SplashKitBackendWASM functions (graphics, audio, input).|
+| `Program.cs`                     | Wasm Bootstrap    |The code provides a basic starting point for browser execution.|
+| `buildAndCopy.sh`                | Build Script      | Shell script that builds the project and copies DLLs and `_framework` files into `../CSharpWasmExpo/`.|
+| `CSharpWasm.csproj`              | Project File      | Targets .NET 8 WebAssembly, includes `Microsoft.CodeAnalysis` (Roslyn).|
+| `Properties/AssemblyInfo.cs`     | Assembly Metadata | Marks supported platform as “browser”.|
+| `Properties/launchSettings.json` | Launch Config     | Settings for running/debugging locally in browser.|
+| `runtimeconfig.template.json`    | Runtime Template  | Template for browser runtime behavior.|
+
+## Prerequisites
+Before starting the build process you need to verify that you have:
+- The .NET 8 SDK needs to be installed on your system.
+- You need to install the WebAssembly tools workload using the command dotnet workload install wasm-tools.
+- Your project folder CSharpWasmExpo requires either a local development environment or a hosting solution to function.
+
+## Build and Copy Process
+You can create and distribute the artifacts through the following command which needs to be executed from the `CSharpWasm/` directory.
+
+```bash
+chmod +x buildAndCopy.sh   # first time only
+./buildAndCopy.sh
+```
+
+This script is responsible for 
+- Building project with `dotnet build`
+- Required DLLs will be copied into the `../CSharpWasmExpo/bin/`
+- WebAssembly runtime files need to be added to the Expo host at a path which depends on your specific setup.
+
+## Usage in the Browser
+
+```C#
+Example of JavaScript call:
+
+const code = 
+using System;
+class Program {
+    static void Main() {
+        Console.WriteLine("Hello from C#!");
+    }
+};
+
+const result = await globalThis.CSharpCodeRunner.CompileAndRun(code);
+console.log(result);
+```
+
+### Output Expected 
+
+```
+Hello from C#!
+```
+
+- The program displays its output in the console after compilation completes successfully.
+- The compiler returns a list of compilation errors when syntax or build problems occur.
+- A program requires a valid entry point which should be static void Main().
+
+## Troubleshooting 
+- No entry point: This means program lacks an entry point which should be defined through `static void Main()`.
+- Error loading assembly: Then build script requires DLLs to exist in the `../CSharpWasmExpo/bin/` directory for successful execution.
+- Check your submitted code lines against the error messages because they show exact locations of the problems.