docs: Update bluetooth overview

Documentation/bluetooth/overview.rst

@@ -7,7 +7,11 @@ Overview
 UUIDs
 -----
 
-UUIDs in use by the card10:
+Bluetooth uses UUIDs to identify almost everything. The Bluetooth SIG specifies a number of "short" 16-bit UUIDs for general use. A device
+is free to define other "long" 128-bit UUIDs if it wants to express non-standard functionality.
+
+The card10 defines a few non-standard UUIDs. They are prefixed with `4232`:
+
 
 +--------------------------------------+-------------------------------+---------------------------------------------------------------------+
 | UUID                                 | Usage                         | Comment                                                             |
@@ -18,6 +22,11 @@ UUIDs in use by the card10:
 +--------------------------------------+-------------------------------+---------------------------------------------------------------------+
 | 422303XX-2342-2342-2342-234223422342 | ECG Service                   | Allows to stream ECG measurements via BLE                           |
 +--------------------------------------+-------------------------------+---------------------------------------------------------------------+
+| 422380XX-2342-2342-2342-234223422342 | Experimental usage            | To be used for development and experiments                          |
++--------------------------------------+-------------------------------+---------------------------------------------------------------------+
+
 
+The first byte after the prefix identifies the service (e.g. `03` for ECG). The next byte is reserved for UUIDs used by the service itself.
+The service uses `00` at this position. The first attribute inside the service uses `01` at this position. See the documentation of any
+service for an example.
 
-UUIDs created for the card10 generally start with `4223`, followed by one byte identifying the service (e.g. `03` for ECG). The next byte is reserved for UUIDs used by the service itself.