Update README.md (#725)

Author: Koenkk

README.md

@@ -24,6 +24,9 @@
     <h1>Official Zigbee2MQTT Home Assistant add-on</h1>
 </div>
 
+> [!CAUTION]
+> If you're using a Raspberry Pi, ensure you have at least a Raspberry Pi 4, as running it on a Raspberry Pi 3 may cause instability due to its limited resources.
+
 ## Installation
 
 1. If you don't have an MQTT broker yet; in Home Assistant go to **[Settings → Add-ons → Add-on store](https://my.home-assistant.io/redirect/supervisor_store/)** and install the **[Mosquitto broker](https://my.home-assistant.io/redirect/supervisor_addon/?addon=core_mosquitto)** add-on, then start it.