Add OpenEnergyMonitor Thermostat docs. (#1889)

* Add OpenEnergyMonitor Thermostat docs.

for home-assistant/home-assistant#5583

* Rename climate.openenergymonitor.markdown to climate.oem.markdown

* remove target temp

source/_components/climate.oem.markdown

@@ -0,0 +1,42 @@
+---
+layout: page
+title: "Open Energymonitor WiFi Thermostat"
+description: "Instructions how to integrate the Open Energy Monitor thermostat with Home Assistant."
+date: 2017-01-27 11:15
+sidebar: true
+comments: false
+sharing: true
+footer: true
+ha_category: Climate
+---
+
+This platform supports the ESP82666 based "WiFi MQTT Relay / Thermostat" sold
+by
+[OpenEnergyMonitor](https://shop.openenergymonitor.com/wifi-mqtt-relay-thermostat/).
+The underlying [library](http://oemthermostat.readthedocs.io/) only supports
+this single relay variant of the [original
+device](https://harizanov.com/2014/12/wifi-iot-3-channel-relay-board-with-mqtt-and-http-api-using-esp8266/).
+
+This platform controls the setpoint of the thermostat in it's "manual" mode,
+therefore there is a configuration option the away setpoint.
+
+To set it up, add the following information to your `configuration.yaml` file:
+
+```yaml
+# Example configuration.yaml entry
+climate oem:
+  - platform: oem
+    name: Home
+    host: 192.168.0.100
+    port: 80
+    away_temp: 14
+```
+
+Configuration variables:
+
+- **host** (*Required*): The IP address or hostname of the thermostat.
+- **port** (*Optional*): The port for the web interface (defaults to 80).
+- **username** (*Optional*): Username for the web interface if set.
+- **password** (*Optional*): Password for the web interface if set.
+- **away_temp** (*Optional*): Setpoint for the thermostat in away mode (defaults to 14 C).
+