Add docs for Flexit A/C platform (#2739)

* Add docs for Flexit A/C platform

* Added note about modbus and a full config example

source/_components/climate.flexit.markdown

@@ -0,0 +1,58 @@
+---
+layout: page
+title: "Flexit A/C controller"
+description: "Instructions how to integrate Flexit A/C unit into Home Assistant."
+date: 2017-06-02 16:30 +0200
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: flexit.png
+ha_category: Climate
+ha_release: 0.47
+ha_iot_class: "Local Polling"
+---
+
+Integrates [Flexit](https://www.flexit.no/en/) Air Conditioning unit into Home Assistant.
+
+Requires an CI66 Modbus Adapter [CI66](https://www.flexit.no/en/products/air_handling_unit/accessories_ahu/modul/modbusadapter_ci66/modbus_adapter_ci66_k2-c2-uni/)
+
+To enable this platform, add the following lines to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+climate:
+  - platform: flexit
+    slave: 21
+```
+
+Configuration variables:
+
+- **slave** (*Required*): The slave ID of the modbus adapter, set using DIP-switches.
+- **name** (*Optional*): Displayed name of the A/C unit
+
+<p class='note'>
+This component requires the [Modbus](/components/modbus/) component to be set up to work
+</p>
+
+Full configuration example including modbus setup shown below:
+
+DIP-switch settings on the CI66:
+1=ON, 2=ON, 3=OFF, 4=ON, 5=OFF, 6=ON, 7=ON, 8=ON
+
+```yaml
+# Full example configuration.yaml entry
+modbus:
+  type: serial
+  method: rtu
+  port: /dev/ttyUSB0
+  baudrate: 56000
+  stopbits: 1
+  bytesize: 8
+  parity: E
+
+climate:
+  - platform: flexit
+    name: Main A/C
+    slave: 21
+```