Added documentation for Bluetooth temperature service

docs/reference/bluetooth/start-temperature-service.md

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+# Bluetooth Temperature Service 
+
+![](/static/bluetooth/Bluetooth_SIG.png)
+
+A micro:bit is able to provide a rough measure of the current environmental temperature. It's an approximation only as in fact the temperature value is inferred from the temperature of its main processor. The Bluetooth temperature service allows another device such as a smartphone to wirelessly find out the micro:bit's current temperature reading or to receive a constant stream of temperature data values. Temperature values are expressed in degrees celsius.
+
+Using the Bluetooth temperature service you could turn your smartphone or tablet into a graphical thermometer using your micro:bit as the sensor. 
+
+No additional code is needed on the micro:bit to use the Bluetooth temperature service from another device.
+
+~~~~sig
+bluetooth.startTemperatureService();
+~~~~
+
+### Example: Starting the Bluetooth temperature service
+
+The following code shows the Bluetooth temperature service being started:
+
+~~~~blocks
+bluetooth.startTemperatureService();
+~~~~
+
+### Video - Temperature service demo - Starts at 3:05
+
+[![micro:bit Bluetooth demo video](/static/bluetooth/microbit_temperature.png)](
+    http://www.youtube.com/watch?v=aep_GVowKfs "Click to launch YouTube video"
+    )
+
+### Advanced
+ 
+For more advanced information on the micro:bit Bluetooth temperature service including information on using a smartphone, see the [Lancaster University micro:bit runtime technical documentation](http://lancaster-university.github.io/microbit-docs/ble/temperature-service/)
+
+### See also
+
+[Bluetooth SIG](https://www.bluetooth.com)
+
+[Bluetooth on micro:bit resources](http://bluetooth-mdw.blogspot.co.uk/p/bbc-microbit.html)
+