Doc: Add note about protocol versions blocking detection.

Since protocol version is picked up now during discovery, the user
might be inclined to trust it. Versions 3.3 and 3.2 are
indistinguishable at this level though, so we always choose the more
common 3.3, which can sometimes be wrong.

Issue #2213

README.md

@@ -224,6 +224,10 @@ time, so you may need to experiment with your automations to see
 whether a single command or multiple commands (with delays, see above)
 work best with your devices.
 
+When adding devices, some devices that are detected as protocol version
+3.3 at first require version 3.2 to work correctly. Either they cannot be
+detected, or work as read-only if the pprotocol is set to 3.3.
+
 ## Heater issues
 
 Goldair GPPH heaters have individual target temperatures for their