Added documentation for on-bluetooth-connected and on-bluetooth-disconnected event handlers

docs/reference/bluetooth/on-bluetooth-disconnected.md

@@ -0,0 +1,33 @@
+# On Bluetooth Disconnected 
+
+![](/static/bluetooth/Bluetooth_SIG.png)
+
+For another device like a smartphone to use any of the Bluetooth "services" which the micro:bit has, it must first connect to the micro:bit. This block starts an [event handler](/reference/event-handler) which in this case will run when a device which is connected to your micro:bit over Bluetooth disconnects.
+
+You could use this event handler to display a letter "D" on the micro:bit LED grid so you know that the Bluetooth connection has been closed.
+
+~~~~sig
+bluetooth.onBluetoothDisconnected(() => {
+});
+~~~~
+
+### Example: Displaying "D" when a Bluetooth connection to the micro:bit is closed
+
+~~~~blocks
+bluetooth.onBluetoothDisconnected(() => {
+    basic.showString("D");
+});
+~~~~
+
+### Video - on Bluetooth disconnected
+
+[![micro:bit Bluetooth demo video](/static/bluetooth/microbit_on_disconnected.png)](
+    http://www.youtube.com/watch?v=HyBcsD9Eh6I "Click to launch YouTube video"
+    )
+
+### See also
+
+[Bluetooth SIG](https://www.bluetooth.com)
+
+[Bluetooth on micro:bit resources](http://bluetooth-mdw.blogspot.co.uk/p/bbc-microbit.html)
+