docs: Update pants build command

[HyeockJinKim]

The path required for the LOCKSET setting has changed when using towncrier, reflect this in the documentation.

Checklist: (if applicable)

• [ ] Milestone metadata specifying the target backport version
• [ ] Mention to the original issue
• [ ] Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• [ ] Update of end-to-end CLI integration tests in ai.backend.test
• [ ] API server-client counterparts (e.g., manager API -> client SDK)
• [ ] Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• [x] Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations

---

📚 Documentation preview 📚: https://sorna--2945.org.readthedocs.build/en/2945/

---

📚 Documentation preview 📚: https://sorna-ko--2945.org.readthedocs.build/ko/2945/