docs: update README with STDIO transport configuration

[CalvinAllen]

Parent Epic

Part of #18 - STDIO Transport Support

Description

Update documentation to explain STDIO transport mode and configuration.

Implementation

Modify: README.md

New Section: STDIO Transport Mode

Add documentation covering:

1. Overview - What STDIO mode is and when to use it
2. Prerequisites - VS must be running with extension loaded
3. Claude Desktop Configuration

{
  "mcpServers": {
    "visual-studio": {
      "command": "path/to/CodingWithCalvin.MCPServer.Server.exe",
      "args": ["--transport", "stdio"]
    }
  }
}

4. Finding the Server.exe path - Typically in VS extension directory
5. Comparison table - HTTP/SSE vs STDIO (when to use each)
6. Limitations - VS must be open first, only one mode at a time

Example Content

## STDIO Transport Mode

For direct integration with Claude Desktop or other MCP clients that spawn 
the server process, you can use STDIO transport instead of HTTP/SSE.

**Important**: Visual Studio must be open with the MCP Server extension 
loaded before starting Claude Desktop with STDIO mode.

### Configuration
...

Acceptance Criteria

• STDIO mode documented in README
• Claude Desktop config example included
• Prerequisites clearly stated
• HTTP vs STDIO comparison
• Path finding instructions