Replace setup instructions with a complete MicroPython deployment procedure

[PurpleSentinel]

Problem

The README instructs users to enter BOOTSEL mode, copy the .py files, then copy the UF2 file. BOOTSEL storage is the UF2 flashing volume, not the MicroPython filesystem used for application modules.

The instructions also omit both JSON files. params.json is mandatory; if it is absent, main.py exits before initializing the display. Following the documented procedure therefore cannot produce a working installation.

Relevant locations

• README.md, Setup
• main.py, file_in(PARAMS_FILE) and early exit
• params.json
• user.json

Acceptance criteria

• Document flashing the correct MicroPython UF2 first.
• Document reconnecting through Thonny, mpremote, or another explicit MicroPython file-transfer tool.
• List every required file, including params.json and the intended handling of user.json.
• Explain that the entry point must be saved as main.py on the device.
• Include a first-boot verification and troubleshooting procedure.
• Test the instructions from a freshly erased board.