Fronius component documentation (#9283)

* Documentation for Fronius sensor component

* Update fronius description

* Fix templating error

* Update doc according to new implementation

* Update configuration description

* Fixes

* Update source/_components/fronius.markdown

Co-Authored-By: nielstron <n.muendler@web.de>

* Update source/_components/fronius.markdown

Co-Authored-By: nielstron <n.muendler@web.de>

* Remove last line

* Simplify example

* Escape yaml templates

* Remove "token" that cannot start any token according to deploy

* Rework description

* Fix configuration strings

* Fix configuration look

* ✏️ Tweaks

* ✏️ Tweak

* Correct documentation

* Change fronius ip to fronius url

* ✏️ Tweak

* ✏️ Use `state_attr()`

source/_components/fronius.markdown

@@ -0,0 +1,98 @@
+---
+title: "Fronius"
+description: "Instructions on how to connect your Fronius Inverter to Home Assistant."
+ha_category:
+  - Energy
+  - Sensor
+logo: fronius.png
+ha_iot_class: Local Polling
+ha_release: 0.96
+---
+
+The `fronius` sensor will poll a [Fronius](http://www.fronius.com/) solar inverter, battery system or smart meter and present the values as sensors (or attributes of sensors) in Home Assistant.
+
+## Configuration
+
+To enable this sensor, add the following lines to your `configuration.yaml` file:
+
+```yaml
+sensor:
+  - platform: fronius
+    resource: FRONIUS_URL
+    monitored_conditions:
+    - sensor_type: inverter
+```
+
+{% configuration %}
+resource:
+  description: "The IP address of the Fronius device"
+  required: true
+  type: string
+monitored_conditions:
+  description: "Conditions to display in the frontend"
+  required: true
+  type: list
+  keys:
+    type:
+      description: "The kind of device, can be one of \"inverter\", \"storage\", \"meter\", or \"power_flow\""
+      required: true
+      type: string
+    scope:
+      description: "The device type for storage and inverter, can be either \"device\" or \"system\""
+      required: false
+      type: string
+      default: "device"
+    device:
+      description: "The id of the device to poll"
+      required: false
+      default: "\"1\" for inverters and \"0\" for other devices such as storages in compliance with Fronius Specs"
+{% endconfiguration %}
+
+## Examples
+
+When including more of the components that one Fronius device offers, 
+a list of sensors that are to be integrated can be given like below.
+
+```yaml
+sensor:
+  - platform: fronius
+    resource: FRONIUS_IP_ADDRESS
+    monitored_conditions:
+    - sensor_type: inverter
+      device: 1
+    - sensor_type: meter
+      scope: system
+    - sensor_type: meter
+      device: 3
+    - sensor_type: storage
+      device: 0
+    - sensor_type: power_flow
+```
+
+## Sensors configuration
+
+To extract more detailed values from the state of each integrated sensor and to circumvent undefined values,
+it is recommended to use template sensors as an interface:
+
+{% raw %}
+```yaml
+- platform: template
+  sensors:
+    electricity_inverter1_power_netto:
+      unit_of_measurement: 'W'
+      value_template: >-
+        {% if states.sensor.fronius_1921684247_inverter_1.attributes.power_ac is defined -%}
+          {{ states_attr('sensor.fronius_1921684247_inverter_1', 'power_ac') | float | round(2) }}
+        {%- else -%}
+          0
+        {%- endif %}
+    electricity_autonomy:
+      unit_of_measurement: '%'
+      value_template: >-
+        {% if states.sensor.fronius_1921684247_power_flow.attributes.relative_autonomy is defined -%}
+          {{ states_attr('sensor.fronius_1921684247_power_flow', 'relative_autonomy') | float | round(2) }}
+        {%- else -%}
+          0
+        {%- endif %}
+```
+{% endraw %}