Documentation for OpenTherm Gateway climate platform (#6118)

* Add documentation for component climate.opentherm_gw

* Update to adhere to standards

* Changed wording from "component" to "device" as it is not a component

* Minor changes

* Add quotes

* Fix location of space

source/_components/climate.opentherm_gw.markdown

@@ -0,0 +1,61 @@
+---
+layout: page
+title: "OpenTherm Gateway"
+description: "Control your OpenTherm Gateway from Home Assistant."
+date: 2018-08-29 16:23
+sidebar: true
+comments: false
+sharing: true
+footer: true
+logo: opentherm.png
+ha_category: Climate
+ha_release: 0.78
+ha_iot_class: "Local Push"
+---
+
+
+The `opentherm_gw` climate platform is used to control the [OpenTherm Gateway](http://otgw.tclcode.com/) from Home Assistant.
+
+# {% linkable_title Configuration %}
+
+```yaml
+# Example configuration.yaml entry
+climate:
+  - platform: opentherm_gw
+    device: /dev/ttyUSB0
+```
+
+{% configuration %}
+device:
+  description: "Path to OpenTherm Gateway device as supported by [PySerial](https://pythonhosted.org/pyserial/url_handlers.html)."
+  required: true
+  type: string
+name:
+  description: The name for the device within Home Assistant.
+  required: false
+  type: string
+  default: OpenTherm Gateway
+precision:
+  description: "The desired precision for this device. Can be used to match your actual thermostat's precision. Supported values are `0.1`, `0.5` and `1.0`."
+  required: false
+  type: float
+  default: "`0.5` for Celsius and `1.0` for Fahrenheit."
+floor_temperature:
+  description: Some thermostats round all temperatures down to the lower value according to their precision. Default behaviour for Home Assistant is to round temperatures to the nearest value. Set this to `True` to override Home Assistant and round to the lower value according to the configured `precision`.
+  required: false
+  type: boolean
+{% endconfiguration %}
+
+# {% linkable_title Example %}
+
+A full configuration example with the OpenTherm Gateway connected to a remote host running `ser2net` looks like the one below.
+
+```yaml
+# Full example configuration.yaml entry
+climate:
+  - platform: opentherm_gw
+    device: socket://otgw.example.org:2345
+    name: Thermostat
+    precision: 0.5
+    floor_temperature: True
+```