Update README.md

Author: DavesCodeMusings

README.md

@@ -47,6 +47,9 @@ See [main.py](main.py) for a more robust example.
 ## Will it run on Microcontroller X?
 If the device has Bluetooth and can run recent versions of MicroPython, it should work.
 
+## What about encryption?
+Sorry. Although [BTHome offers encrypted communication](https://bthome.io/encryption/), the [MicroPython AES encryption](https://docs.micropython.org/en/latest/library/cryptolib.html) implementation does not support the CCM mode required for BTHome encryption.
+
 ## Can it do more than temperature and humidity?
 My goal was to create an outdoor sensor to measure temperature, humidity, and illuminance so I could make automation decsions in Home Assistant. I've included nearly the entire list of object_ids described in the [BTHome v2 format](https://bthome.io/format), but those outside of temperature, humidity, and battery level are untested in real world scenarios.