Add Atla MCP server to README

[jacksongolden]

Description

Add link to official Atla MCP server: https://github.com/atla-ai/atla-mcp-server

Server Details

• Server:
• Changes to:

Motivation and Context

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)
• [x] Documentation update

Checklist

• [x] I have read the MCP Protocol Documentation
• [ ] My changes follows MCP security best practices
• [x] I have updated the server's README accordingly
• [x] 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