docs: add CoinStats MCP server to official integrations in README

[nargit21]

Description

Added a new MCP server integration for CoinStats, enabling secure access to cryptocurrency market data, portfolio tracking, and news via the CoinStats API. This server can be used by LLM clients and supports both NPX and Docker usage.

Server Details

• Server: coinstats-mcp
• Changes to: Added entry to README.

Motivation and Context

This change adds support for a popular crypto API, allowing developers and AI agents to securely retrieve portfolio data and market information using MCP conventions. It expands the set of financial data sources available, and solves the gap for CoinStats users wanting native MCP support.

How Has This Been Tested?

Tested locally with multiple MCP clients (NPX and Docker deployment) using a valid CoinStats API key. Verified core endpoints work for market data, portfolio fetching, and news retrieval. No breaking changes identified.

Breaking Changes

No breaking changes. The new server does not alter interfaces or affect current MCP configurations.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have read the MCP Protocol Documentation
• My changes follows MCP security best practices
• I have updated the server's README accordingly
• I have tested this with an LLM client
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have documented all environment variables and configuration options

Additional context

CoinStats MCP provides access via API key and supports both usage through NPX and Docker, as described in its README.