fix: Set Gemini 2.5 Pro Preview as default and improve portability

Changes:
- Restored Gemini 2.5 Pro Preview as the default model
- Removed hardcoded paths from claude_config_example.json
- Added MCP_DISCOVERY.md explaining how Claude discovers MCP servers
- Updated README with natural language usage examples

The server now defaults to the most capable Gemini 2.5 Pro Preview model
as requested, and all paths are now relative for better portability.

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

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

claude_config_example.json

@@ -1,8 +1,8 @@
 {
   "mcpServers": {
     "gemini": {
-      "command": "/Users/fahad/Developer/gemini-mcp-server/venv/bin/python",
-      "args": ["/Users/fahad/Developer/gemini-mcp-server/gemini_server.py"],
+      "command": "/path/to/gemini-mcp-server/venv/bin/python",
+      "args": ["/path/to/gemini-mcp-server/gemini_server.py"],
       "env": {
         "GEMINI_API_KEY": "your-gemini-api-key-here"
       }