Add USAGE_GUIDE.md for CPF Toolbox

[pranusha-2299]

Summary

• Add USAGE_GUIDE.md — a self-contained guide for building CPM bundles with the CPF Toolbox
• Rename README.md → OLD_README.md to preserve the original project documentation

Guide contents

• Prerequisites — Java/Maven requirements, Maven dependencies, Java imports
• Section 0 — What the toolbox does (traversal only, not domain-specific)
• Section 1 — 3-step workflow (deserialize → add domain part → serialize)
• Section 2 — Building input JSON templates with field reference, minimal example, and realistic biobank example
• Section 3 — Must-have checklist (what breaks if missing)
• Section 4 — Must-not checklist (common mistakes with real wrong-way output)
• Section 5 — Adding the domain-specific part via ProvToolBox API with full Java example and verified output
• Section 6 — FAQ and common errors (thrown exceptions + silent issues)

All JSON outputs in the guide are verified — generated by running the toolbox, not hand-crafted.

Test plan

• Verify USAGE_GUIDE.md renders correctly on GitHub (tables, collapsible sections, code blocks)
• Confirm OLD_README.md content matches the original README.md

🤖 Generated with Claude Code

[pranusha-2299]

Opened against wrong repo — meant for Common-Provenance-Framework/CPF-Toolbox