Add heat meter docs for Powerfox integration (#36738)

source/_integrations/powerfox.markdown

@@ -40,7 +40,7 @@ Not all Poweropti devices are supported currently. Check the list below to see i
 | PB 202001             | Power meter | Not tested |
 | WA 201902             | Water meter | Yes        |
 | Powerfox FLOW         | Gas meter   | No         |
-| HA 201902             | Heat meter  | No         |
+| HA 201902             | Heat meter  | Yes        |
 
 ## Data updates
 
@@ -76,6 +76,15 @@ It will create the following sensors:
 - **Cold water (m³)**: How much cold water is used.
 - **Warm water (m³)**: How much warm water is used.
 
+### Heat meter
+
+It will create the following sensors:
+
+- **Total eneregy (kWh)**: How much energy is used.
+- **Delta energy (kWh)**: How much energy is used since the last update.
+- **Total volume (m³)**: How much water is used.
+- **Delta volume (m³)**: How much water is used since the last update.
+
 ## Troubleshooting
 
 There are no commonly known issues with this integration.