docs: sync README config example with scaffolded defaults

[jroell]

Summary

• sync the README.md config example with the actual gg init scaffold from src/config.ts
• fix malformed Markdown table rows in the Pair Mode Options and Use Cases sections so they render correctly

Why

The README config snippet had drifted from the code-backed source of truth in src/config.ts. It still showed a duplicated timeoutMs key, the old 600000 timeout value, and omitted the _readme field that gg init actually writes.

Source references

• b716fa2 — docs: sync defaults and benchmark notes (#5)
• d5da97c — feat: retry-on-early-exit, test-script bootstrap, byte-level verification, model updates for terminal-bench 2.0
• e360ddf — feat: 'gg init' scaffolds .gitgang/config.json with per-repo defaults

Validation

• reviewed the README diff against src/config.ts
• confirmed the malformed || table rows are gone from README.md
• no other recent significant user-facing doc gaps were found in the latest source history

Context

• Conversation: https://app.warp.dev/conversation/96fdc70d-2a9d-4e69-9c05-3d36144c0c40
• Run: https://platform.warp.dev/runs/01a0a527-3263-759d-b862-3122c3554363