Add GitHub Communication & Collaboration Guide to README

[Copilot]

This PR addresses the question "can msg to other person via github?" by adding a comprehensive communication guide to the README.

What's Added

A new "GitHub Communication & Collaboration" section that explains:

Available Communication Methods on GitHub:

1. Issues - For asking questions about specific problems, discussing algorithms, and reporting bugs
2. Pull Request Comments - For code reviews and implementation discussions
3. Repository Discussions - For broader conversations and sharing experiences
4. Commit Comments - For feedback on specific changes

Best Practices for Communication:

• Guidelines for respectful and effective communication
• How to use @mentions to tag contributors
• Importance of searching existing issues before posting

Getting Help with LeetCode Problems:

• Step-by-step guide for opening issues with coding questions
• How to include context and current approach when stuck
• Tips for engaging with the community

Why This Matters

While GitHub doesn't have traditional direct messaging like social platforms, it offers powerful collaboration tools that many developers aren't fully aware of. This guide helps users understand how to:

• Get help with challenging LeetCode problems
• Collaborate on better solutions
• Build connections within the coding community
• Follow best practices for open source communication

The new section fits naturally with the repository's existing "Community Engagement" theme and provides practical value for developers looking to learn and collaborate.

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