docs: one-pager 'Try MCP in Cursor' for aimarket-mcp + oracle-gateway

[alexar76]

Why

Profile and Glama send people here; they need a Cursor-specific paste, not a full ecosystem tour.

Task

Add docs/quickstart-mcp-cursor.md (EN only is fine) with:

1. Install aimarket-mcp via PyPI (pip install aimarket-mcp)
2. Cursor mcp.json snippet (stdio)
3. One-line smoke: call web_search with query site:modelmarket.dev
4. Optional second block for aimarket-oracle-gateway pointing at live Hub URL

Acceptance

• File linked from root README under a single bullet
• Snippets copy-paste clean (no /path/to without a note)
• Under 80 lines