Mention the possibility of missing energy sensor (home-assistant#12085)

Relatively recent devices do not necessarily have the energy metering
capabilities which can be surprising. The possibility of lacking
properties due to device capabilities as well as the possibility of
missing energy sensor in bold.

source/_integrations/melcloud.markdown

@@ -47,7 +47,7 @@ token:
 
 ## Air-to-Air device
 
-An Air-to-Air heat pump provides `climate` and `sensor` platforms.
+An Air-to-Air heat pump provides `climate` and `sensor` platforms. Device capabilities can limit the available parameters and sensors.
 
 ### Climate
 
@@ -63,4 +63,4 @@ The following parameters can be controlled for the `climate` platform entities:
 The following attributes are available for `sensor` platform entities:
 
 - Room temperature
-- Energy - The total consumed energy in kWh.
+- Energy - The total consumed energy in kWh. **Not supported by all models.**