Update PlutoSDR example config defaults

docs/config.plutosdr.json

@@ -35,6 +35,7 @@
     "limiterEnabled": true,
     "limiterCeiling": 1,
     "fmModulationEnabled": true,
+    "watermarkEnabled": false,
     "mpxGain": 1,
     "bs412Enabled": true,
     "bs412ThresholdDBr": 0,