DOC-5: tell installers to turn on the Supervisor Watchdog

Since SAFETY-61 a dead control loop writes 0 W and exits 70. The Supervisor
restarts a stopped add-on only when the per-install Watchdog toggle is on,
and it defaults to off. One step in DOCS.md "Before you start", with a
pointer to the DECISIONS file.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BwRLw7eKYj2byVdwB6kbjU

goodwe_controller/DOCS.md

@@ -16,6 +16,11 @@ You need:
 - A T-CAN485 (ESP32) flashed with `firmware/goodwe-master.yaml`
 - A grid-power sensor already working in Home Assistant, updating every ~5–10 s
 
+After installing, turn on **Watchdog** on the add-on's Info tab. A crashed
+control loop stops the add-on at 0 W, and the Supervisor restarts it only when
+Watchdog is on (it is off by default). See
+`DECISIONS/SAFETY-61-control-task-death.md`.
+
 ## The safety model, in short
 
 The inverter **holds its last command forever** — it has no meter-timeout. So: