docs: ble: Add links and fix formatting

Link to other BLE documentation and fix monospace formatting.

Documentation/bluetooth/card10.rst

+.. _bluetooth_card10_service:
+
 Bluetooth Card10 Service
 ========================
 

Documentation/bluetooth/ecg.rst

+.. _bluetooth_ecg_service:
+
 Bluetooth ECG Service
 ========================
 

Documentation/bluetooth/file-transfer.rst

+.. _bluetooth_file_transfer:
+
 Bluetooth File Transfer
 =======================
 

Documentation/bluetooth/overview.rst

@@ -3,32 +3,32 @@
 Overview
 ========
 
-
 UUIDs
 -----
+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.
 
-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`:
+The card10 defines a few non-standard UUIDs. They are prefixed with ``4232``:
 
 
-+--------------------------------------+-------------------------------+---------------------------------------------------------------------+
++--------------------------------------+-------------------------------------------------------+--------------------------------------------------------------------+
 | UUID                                 | Usage                                                 | Comment                                                            |
-+======================================+===============================+=====================================================================+
-| 422301XX-2342-2342-2342-234223422342 | File Transfer Service         | Used by the Companion App to install apps on the card10             |
-+--------------------------------------+-------------------------------+---------------------------------------------------------------------+
-| 422302XX-2342-2342-2342-234223422342 | card10 Service                | Controls general card10 functionality like LEDs and personal state  |
-+--------------------------------------+-------------------------------+---------------------------------------------------------------------+
-| 422303XX-2342-2342-2342-234223422342 | ECG Service                   | Allows to stream ECG measurements via BLE                           |
-+--------------------------------------+-------------------------------+---------------------------------------------------------------------+
++======================================+=======================================================+====================================================================+
+| 422301XX-2342-2342-2342-234223422342 | :ref:`File Transfer Service<bluetooth_file_transfer>` | Used by the Companion App to install apps on the card10            |
++--------------------------------------+-------------------------------------------------------+--------------------------------------------------------------------+
+| 422302XX-2342-2342-2342-234223422342 | :ref:`card10 Service<bluetooth_card10_service>`       | Controls general card10 functionality like LEDs and personal state |
++--------------------------------------+-------------------------------------------------------+--------------------------------------------------------------------+
+| 422303XX-2342-2342-2342-234223422342 | :ref:`ECG Service<bluetooth_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.
+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.
 
-You can use the UUID range 422380XX-2342-2342-2342-234223422342 for your own experiments / demos/ development. For example the demos under `demos/` in
-the repository use this range of UUIDs.
+You can use the UUID range 422380XX-2342-2342-2342-234223422342 for your own
+experiments / demos/ development. For example the demos under `demos/` in the
+repository use this range of UUIDs.