docs: add guide for capturing BLE data to support new devices

[bluetoothbot]

What

A contributor guide (docs/adding-device-support.md) explaining how to capture
the raw Bluetooth data the library needs to add a new device or feature, linked
from the README.

Why

A steady stream of device-support issues stalls for one reason: nobody has
captured the raw advertisement/GATT bytes the parser needs. There was no
documented self-serve path for non-coders to contribute that data, so the same
"how/what do I capture?" gets re-explained per issue (or never). This turns the
recurring blocker into a single referenceable page.

How

• Documents what adv_parser.py actually dispatches on: the SwitchBot service
  UUIDs + model byte, and the manufacturer-data company IDs (2409/741/89).
• Three capture paths: nRF Connect, a BleakScanner snippet, and Android HCI
  snoop logs for connection-level command features.
• Uses the public parse_advertisement_data() to verify recognition.
• Includes a "currently needed captures" table mapping five open issues
  (Feature Request: night light control for ceiling light / pro #490, [bug] Cannot see or remove password in Switchbot App if added to Keypad with add_password. #447, Support for Switchbot Keypad Touch #439, Switchbot Meter Pro time synchronisation #416, Feature request: Bot schedules #345) to the exact capture each needs.

Testing

Docs-only — no code paths changed. Verified the referenced symbols
(SUPPORTED_TYPES, service UUIDs, company IDs, parse_advertisement_data
signature) against the current source.

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Autonomous PR by Kōan, on behalf of @bdraco / the OpenHome team (nick@openhomefoundation.org).

---

Quality Report

Changes: 2 files changed, 135 insertions(+)

Code scan: 4 issue(s) found

• docs/adding-device-support.md:62 — debug print statement
• docs/adding-device-support.md:64 — debug print statement
• docs/adding-device-support.md:65 — debug print statement
• docs/adding-device-support.md:82 — debug print statement

Tests: passed (1300 passed)

Branch hygiene: clean

Generated by Kōan

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