Docs: Add Star History chart to README.md (#99)

Hi there,

I noticed that many popular open-source projects include a star history chart in their README to visualize community growth and engagement. I thought it would be a great addition to this project as well.

This PR adds a dynamic Star History chart to the end of the `README.md`.

### Example
This is what the chart will look like:

[![Star History Chart](https://api.star-history.com/svg?repos=BeehiveInnovations/zen-mcp-server&type=Date)](https://www.star-history.com/#BeehiveInnovations/zen-mcp-server&Date)

It's a small, non-intrusive addition that adds a nice touch to the project's landing page.

README.md

@@ -516,4 +516,8 @@ Built with the power of **Multi-Model AI** collaboration 🤝
 - [MCP (Model Context Protocol)](https://modelcontextprotocol.com) by Anthropic
 - [Claude Code](https://claude.ai/code) - Your AI coding assistant & orchestrator
 - [Gemini 2.5 Pro & 2.0 Flash](https://ai.google.dev/) - Extended thinking & fast analysis
-- [OpenAI O3](https://openai.com/) - Strong reasoning & general intelligence
+- [OpenAI O3](https://openai.com/) - Strong reasoning & general intelligence
+
+### Star History
+
+[![Star History Chart](https://api.star-history.com/svg?repos=BeehiveInnovations/zen-mcp-server&type=Date)](https://www.star-history.com/#BeehiveInnovations/zen-mcp-server&Date)