docs: Add PlantUML diagram of the demo setup

Show Dashboard/SmartHome demo setup on a puml diagram.

Signed-off-by: Zbigniew Bodek <zbigniew.bodek@huawei.com>

docs/demos/assets/smart-home-demo-arch.puml

+' SPDX-FileCopyrightText: Huawei Inc.
+'
+' SPDX-License-Identifier: CC-BY-4.0
+
+@startuml smarthome-demo-arch
+!include https://raw.githubusercontent.com/plantuml-stdlib/C4-PlantUML/master/C4_Context.puml
+
+HIDE_STEREOTYPE()
+
+title SmartHome demo architecture
+
+Person(user, "User")
+System(dashboard, "Dashboard", "Home Assistant software running on Avenger96 board, interfacing with the user via a touchscreen")
+
+System_Ext(sensors_board, "Sensors board", "96Boards Nitrogen with the Sensors Mezzanine adapter and selected sensors connected")
+System_Ext(smart_bulb, "Smart bulb/LED", "96Boards Nitrogen with the Sensors Mezzanine adapter and LED connected")
+
+Rel(user, dashboard, "Uses")
+Rel_Back(dashboard, sensors_board, "Sends sensors readings", "BLE")
+Rel_Neighbor(dashboard, sensors_board, "Reads out sensors", "BLE")
+Rel(dashboard, smart_bulb, "Controls", "BLE")
+@enduml

docs/demos/smart-panel.rst

@@ -20,6 +20,8 @@ HomeAssistant. The gateway also provides UI as a browser connected to the
 localhost HomeAssistant server. The gateway is connected over Bluetooth to two
 Nitrogen boards exposing sensors and/or emulating device (e.g. light bulbs).
 
+.. image:: assets/smart-home-demo-arch.png
+
 How to build
 ************