Add note for why using 0x15

Author: chengweih001

index.bs

@@ -5544,6 +5544,11 @@ The [=remote end steps=] with command parameters |params| are:
     [=associated Bluetooth=].
 1. If |simulatedDeviceInstance|.{{[[gatt]]}}.{{[[automatedGATTConnectionResponse]]}} is `"expected"`,
     set |simulatedDeviceInstance|.{{[[gatt]]}}.{{[[automatedGATTConnectionResponse]]}} to `0x15`.
+    <div class="note">
+      `0x15` represents `"Remote Device Terminated Connection due to Power Off"` according to the
+      <a>List of Error Codes</a>. This allows a simulation scenario where the Bluetooth device is
+      not able to respond to a GATT connection attempt.
+    </div>
 1. Otherwise, <a>clean up the disconnected device</a> |simulatedDeviceInstance|.
 
 </div>