Add documentation for units for energy by distance (#2548)

Author: jschlyter

docs/core/entity/number.md

@@ -45,6 +45,7 @@ If specifying a device class, your number entity will need to also return the co
 | `NumberDeviceClass.DATA_SIZE` | bit, kbit, Mbit, Gbit, B, kB, MB, GB, TB, PB, EB, ZB, YB, KiB, MiB, GiB, TiB, PiB, EiB, ZiB, YiB | Data size
 | `NumberDeviceClass.DISTANCE` | km, m, cm, mm, mi, yd, in | Generic distance
 | `NumberDeviceClass.ENERGY` | J, kJ, MJ, GJ, mWh, Wh, kWh, MWh, GWh, TWh, cal, kcal, Mcal, Gcal | Energy, this device class should used to represent energy consumption, for example an electricity meter. Represents _power_ over _time_. Not to be confused with `power`.
+| `NumberDeviceClass.ENERGY_DISTANCE` | kWh/100km, mi/kWh, km/kWh | Energy per distance, this device class should be used to represent energy consumption by distance, for example the amount of electric energy consumed by an electric car.
 | `NumberDeviceClass.ENERGY_STORAGE` | J, kJ, MJ, GJ, mWh, Wh, kWh, MWh, GWh, TWh, cal, kcal, Mcal, Gcal | Stored energy, this device class should be used to represent stored energy, for example the amount of electric energy currently stored in a battery or the capacity of a battery. Represents _power_ over _time_. Not to be confused with `power`.
 | `NumberDeviceClass.FREQUENCY` | Hz, kHz, MHz, GHz | Frequency
 | `NumberDeviceClass.GAS` | m³, ft³, CCF | Volume of gas. Gas consumption measured as energy in kWh instead of a volume should be classified as energy.

docs/core/entity/sensor.md

@@ -48,6 +48,7 @@ If specifying a device class, your sensor entity will need to also return the co
 | `SensorDeviceClass.DISTANCE` | km, m, cm, mm, mi, nmi, yd, in | Generic distance
 | `SensorDeviceClass.DURATION` | d, h, min, s, ms | Time period. Should not update only due to time passing. The device or service needs to give a new data point to update.
 | `SensorDeviceClass.ENERGY` | J, kJ, MJ, GJ, mWh, Wh, kWh, MWh, GWh, TWh, cal, kcal, Mcal, Gcal | Energy, this device class should be used for sensors representing energy consumption, for example an electricity meter. Represents _power_ over _time_. Not to be confused with `power`.
+| `SensorDeviceClass.ENERGY_DISTANCE` | kWh/100km, mi/kWh, km/kWh | Energy per distance, this device class should be used to represent energy consumption by distance, for example the amount of electric energy consumed by an electric car.
 | `SensorDeviceClass.ENERGY_STORAGE` | J, kJ, MJ, GJ, mWh, Wh, kWh, MWh, GWh, TWh, cal, kcal, Mcal, Gcal | Stored energy, this device class should be used for sensors representing stored energy, for example the amount of electric energy currently stored in a battery or the capacity of a battery. Represents _power_ over _time_. Not to be confused with `power`.
 | `SensorDeviceClass.ENUM` | | The sensor has a limited set of (non-numeric) states. The `options` property must be set to a list of possible states when using this device class.
 | `SensorDeviceClass.FREQUENCY` | Hz, kHz, MHz, GHz | Frequency