docs: Add labels for supported hardware

This gives us the ability to easily reference them in various other parts (eg. release notes).

Signed-off-by: Andrei Gherzan andrei.gherzan@huawei.com

docs/hardware-support/boards/raspberrypi4.rst

@@ -15,6 +15,12 @@ Raspberry Pi 4 Model B
 Overview
 ********
 
+.. note::
+
+   Even though this documentation targets Raspberry Pi 4, in Oniro, the same
+   image provides support for Raspberry Pi 3 as well. This means that the
+   following considerations and instructions apply to both types of hardware.
+
 Raspberry Pi 4 Model B is powered with Broadcom BCM2711, quad-core Cortex-A72
 (ARM v8) 64-bit SoC @ 1.5GHz. This product's key features include a
 high-performance 64-bit quad-core processor, dual-display support at