Add documentation for Model Context Protocol (MCP)

Description

We need to add documentation for the recently implemented Model Context Protocol (MCP) support in the mycoder project. The documentation should explain what MCP is, how it's configured in mycoder, and how to use it.

Requirements

• Create a new page in the usage section of the docs
• Explain what the Model Context Protocol is and its benefits
• Document how to configure MCP in mycoder
• Provide examples of using MCP with mycoder
• Include references to the official MCP website (https://modelcontextprotocol.io) and SDK (https://www.npmjs.com/package/@modelcontextprotocol/sdk)

References

• MCP implementation is in the sibling project at ../mycoder/packages/agent/src/core/mcp
• MCP tool implementation is at ../mycoder/packages/agent/src/tools/mcp.ts
• MCP configuration is documented in the CLI README at ../mycoder/packages/cli/README.md