docs: add community example — trustless USDC agents (OOAK + zkML)

[hshadab]

• Summary
  • Adds a “Community Examples” section to README pointing to a community-maintained OOAK + zkML example that gates secure tools with verifiable checks (ONNX → Groth16 → on-chain verify) before executing USDC actions.
  • Adds a brief one‑pager under docs/community-examples with context and links.
• Motivation
  • Complements the OOAK launch by showcasing a trustless pattern for autonomous payments, while keeping this repo vendor‑neutral and lean.
• Changes
  • README: add “Community Examples”; fix “exmple” typo; fix GitHub example path.
  • New doc: docs/community-examples/agentkit-circle-ooak.md.
• How To Verify
  • Open README and follow the link; open the docs page for additional context.
  • Docs‑only; no API/runtime changes.
• Related Links
  • OOAK blog (Mira Belenkiy): https://www.circle.com/blog/ooak-object-oriented-agent-kit
  • Community example: https://github.com/hshadab/agentkit/tree/main/Circle-OOAK
• Checklist
  • Docs-only change
  • Follows README style
  • No runtime changes
  • Community attribution