docs: add ClaudePost to community servers list

[ZilongXue]

This PR updates the community server list by adding the ClaudePost MCP server.

Description

Add a new MCP server link and description for ClaudePost. ClaudePost enables seamless email management for Gmail, offering secure features like email search, reading, and sending.

Server Details

• Server: ClaudePost
• Changes to: Readme.md

Motivation and Context

ClaudePost provides users with an email management server that integrates seamlessly with Gmail.

How Has This Been Tested?

Tested ClaudePost on Claude Desktop to ensure proper functionality, including email search, reading, and sending.

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