add Nx MCP to the list of MCP servers

[juristr]

Description

This PR just adds the Nx MCP to the list of official MCP servers in the README. The linked README has all the details. There's more about what the MCP does on our docs.

Server Details

(not modifying any server, just updating READMEs)

Motivation and Context

I found the list of MCP servers useful and figured I'd contribute the one I'm working on.

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

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