README: add personal motivation and AI disclosure sections

[modfox]

Adds two README sections:

• Why I built this — a short, first-person note on the motivation: macOS-beta driver breakage (macOS 27), the flaky plug/replug behavior, and avoiding Wacom's eventual end-of-life of the tablet.
• AI disclosure — makes clear the project was built with the help of Claude (via Claude Code), under my direction and review, and that the clean-room reverse engineering was documented from the device's own observable behavior.

Docs-only change; no code touched.

🤖 Generated with Claude Code