place note on future 8MB flash requirement prominently

docs/hardware/index.md

@@ -11,6 +11,10 @@ Please see the [inverter overview](inverter_overview.md) to see if your inverter
 
 For an easy start, use a "NodeMCU32 ESP32 DEVKIT DOIT" or "[ESP32 NodeMCU Development Board](esp32nodemcu_38pin.md)" with an ESP32-S3 or ESP-WROOM-32 chipset on it.
 
+!!! note "Upstream Project"
+
+    Due to the growing size of the code and the memory limitations of the common ESP32 boards (4Mb Flash) on the market today, we expect sometime in the future that ESP32 boards with minimum 8Mb will be necessary to run the OpenDTU-OnBattery code. Such boards have the ESP32-S3 and including -N8R, -N16R, -N32R indicating 8MB,16Mb or 32Mb Flash memory respectively.
+
 Sample Picture:
 
 ![NodeMCU-ESP32](../assets/images/nodemcu-esp32.png)