support for buffer signature (#325)

docs/reference/bluetooth/advertise-uid.md

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+# Avertise UID
+
+Advertises a UID via the Eddystone protocol over Bluetooth.
+
+## ~hint
+
+### Eddystone
+
+Bluetooth beacons are used to indicate proximity to a place or object of interest. 
+Beacons use Bluetooth advertising to broadcast a small amount of data, 
+which can be received and acted upon by anyone in range with a suitable device and software, typically a smartphone and application.
+
+There are various beacon message formats, which define the way Bluetooth advertising packets are used as containers for beacon data. 
+iBeacon is Apple's beacon message format. Eddystone comes from Google.
+
+Read more at https://lancaster-university.github.io/microbit-docs/ble/eddystone/ .
+
+## ~
+
+```sig
+bluetooth.advertiseUid(42, 1, 7, true);
+```
+
+### Parameters
+
+* ``namespace`` last 4 bytes of the namespace uid (6 to 9)
+* ``instance`` last 4 bytes of the instance (2 to 5)
+* ``power`` - a [number](/reference/types/number) representing the power level between 0 (short) and 7 (maximum range).
+* ``connectable`` - a [boolean](/reference/type/boolean) indicating whether or not the micro:bit should accept connections. 
+
+## Encoding
+
+The bytes of ``namespace`` and ``instance`` are encoded to generate the 10 bytes UID namespace and 6 bytes UID instance.
+
+```
+UID namespace: [0, ..., namespace]
+UID instance: [0, ..., instance]
+```
+
+## See Also
+
+[stop-advertising](/reference/bluetooth/stop-advertising), [advertise-uid-buffer](/reference/bluetooth/advertise-uid-buffer)
+
+```package
+bluetooth
+```