Move archived servers to archived.md instead of deleting

Instead of completely removing the archived servers section, move it to a
dedicated archived.md file with a reference from the README.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -30,6 +30,10 @@ These servers aim to demonstrate MCP features and the official SDKs.
 - **[Sequential Thinking](src/sequentialthinking)** - Dynamic and reflective problem-solving through thought sequences.
 - **[Time](src/time)** - Time and timezone conversion capabilities.
 
+### Archived
+
+For archived reference servers, see [archived.md](archived.md).
+
 ## 🤝 Third-Party Servers
 
 ### 🎖️ Official Integrations