docs: fix MCP server config example to match the loader (mcp.servers, not mcpServers)

[ken-jo]

What does this PR do?

The README points MCP users at .grok/settings.json with an mcpServers key, but loadMcpServers() (src/utils/settings.ts) reads them from ~/.grok/user-settings.json under a nested mcp.servers array (return loadUserSettings().mcp?.servers ?? []). So following the README puts servers under the wrong key in the wrong file, and they silently never load.

This corrects the feature-table reference (file + key) and adds a short example using the real McpServerConfig shape (id, label, enabled, transport, plus the stdio/http fields). Docs-only — no loader or runtime change.

(No tracking issue — direct documentation correction.)

Checklist

• I tested my changes — verified the documented file/key/shape against loadMcpServers() and the McpServerConfig interface in src/utils/settings.ts
• I reviewed my own code

🤖 Generated with Claude Code

[open-cla]

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[superagent-security]

Superagent didn't find any vulnerabilities or security issues in this PR.