Add Entity categories for Home Assistant (#2636)

esphome/components/xiaomi_lywsd03mmc/sensor.py

@@ -6,6 +6,7 @@ from esphome.const import (
     CONF_HUMIDITY,
     CONF_MAC_ADDRESS,
     CONF_TEMPERATURE,
+    ENTITY_CATEGORY_DIAGNOSTIC,
     STATE_CLASS_MEASUREMENT,
     UNIT_CELSIUS,
     UNIT_PERCENT,
@@ -49,6 +50,7 @@ CONFIG_SCHEMA = (
                 accuracy_decimals=0,
                 device_class=DEVICE_CLASS_BATTERY,
                 state_class=STATE_CLASS_MEASUREMENT,
+                entity_category=ENTITY_CATEGORY_DIAGNOSTIC,
             ),
         }
     )