Add section to ReadMe.md for setting up for energy dashboard (#79)

* Update README.md

* Update TOC of ReadMe.md

* Changed chapter name in Readme

* Formal changes in enegry section in ReadMe

* Formal changes in energy section in ReadMe #2

Author: NachtaktiverHalbaffe

README.md

@@ -24,6 +24,8 @@ Power sensors can be created for `light`, `switch`, `fan`, `binary_sensor`, `inp
 - [Light model library](#light-model-library)
     - [LUT data files](#lut-data-files)
     - [Supported models](#supported-models)
+- [Setting up for energy dashboard](#setting-up-for-energy-dashboard)
+    - [Creating energy groups](#creating-energy-groups)   
 - [Debug logging](#debug-logging)
 
 ## Installation
@@ -307,6 +309,51 @@ python3 measure.py
 
 See the [list](docs/supported_models.md) of supported lights which don't need any manual configuration
 
+## Setting up for energy dashboard
+If you want to use this power sensors with the new [energy integration](https://www.home-assistant.io/blog/2021/08/04/home-energy-management/), you have to create a energy sensor which utilizes the power of the powercalc sensor. This can be done with the [Riemann integration integration](https://www.home-assistant.io/integrations/integration/), which calculates the energy and since release 2021.8 this integration can natively be used in the energy dashboard. An example configuration, which you have to copy into your `configuration.yaml`, can be seen below (assuming you have a powercalc sensor with entity_id `sensor.kingkong_power`:
+
+````yaml
+sensor:
+    - platform: integration
+      source: sensor.kingkong_power
+      name: kingkong_power_kWh
+      unit_prefix: k
+      round: 2
+````
+If you are tired of writing out all these configuration, you can use the template below. Just copy the template into the template section in the developer tools. Then this template creates the configuration of all the power sensors you have (so not just the powercalc ones) which you can copy to your `configuration.yaml` (or only the parts you need).
+
+````yaml
+{% for state in states -%}
+{%- if state.attributes.unit_of_measurement == "W" and state.attributes.device_class == "power" -%}
+- platform: integration
+  source: {{ state.entity_id }}
+  unit_prefix: k
+  round: 2
+{% endif -%}
+{%- endfor -%}
+````
+
+### Creating energy groups
+If you want to sum up all energy usage from one category e.g. all of your servers, then create a powercalc sensor and an integration sensor for each of these servers like described in the section before. Then you create a template energy usage sensor which sums up all values of the energy sensors (a example sensor can be found below). It's essential to add the attributes `last_reset`, `state_class` and `device_class` because these are needed for the sensor to be compatible with the energy integration.  
+
+````yaml
+- platform: template
+  sensors:
+    energy_server:
+      friendly_name: "Alle Server Energieverbrauch"
+      unit_of_measurement: kWh
+      value_template: >-
+        {{states('sensor.kingkong_power_kwh') | float + states('sensor.kinglouie_power_kwh') | float}}
+      attribute_templates:
+        last_reset: "1970-01-01T00:00:00+00:00"
+        state_class: measurement
+        device_class: energy
+        icon: mdi:counter
+````
+> **Don't** create a template sensor which sums up all values from the power sensors and use this sensor to create a energy sensor because this won't work as you would expect. It 
+> wouldn't update in regular bases and as a consequence wont be shown in the energy dashboard in the right timeslots.
+
+
 ## Debug logging
 
 Add the following to configuration.yaml: