samples: Bluetooth: df_tx: Add information about nRF5340 to README.rst

Add information about support of nRF5340 SOC in the sample
README.rst.

Signed-off-by: Piotr Pryga <[email protected]>

Author: ppryga-nordic

samples/bluetooth/direction_finding_connectionless_tx/README.rst

@@ -13,6 +13,7 @@ functionality by sending Constant Tone Extension with periodic advertising PDUs.
 Requirements
 ************
 
+* nRF5340DK board
 * nRF52833DK board with nRF52833 SOC
 * nRF52833DK board with nRF52820 SOC
 * antenna matrix for AoD (optional)
@@ -36,6 +37,21 @@ To use Angle of Arrival mode only, build this application as follows:
    :goals: build flash
    :compact:
 
+To run the application on nRF5340DK there must be provided a child image aimed to
+run on network core. :zephyr_file:`samples/bluetooth/hci_rpmsg` sample application
+may be used for that purpose.
+
+To build :zephyr_file:`samples/bluetooth/hci_rpmsg` sample with direction finding
+support enabled:
+
+* create :zephyr_file:`samples/bluetooth/hci_rpmsg/boards/nrf5340dk_nrf5340_cpunet.overlay`
+  with the same content as :zephyr_file:`samples/bluetooth/direction_finding_connectionless_tx/
+  boards/nrf52833dk_nrf52833.overlay`
+* create :zephyr_file:`samples/bluetooth/hci_rpmsg/boards/nrf5340dk_nrf5340_cpunet.conf`
+  file. Copy content of :zephyr_file:`samples/bluetooth/direction_finding_connectionless_tx/boards/
+  nrf52833dk_nrf52833.conf. Add CONFIG_BT_EXT_ADV=y configuration entry to enable extended size
+  of :code:`CONFIG_BT_BUF_CMD_TX_SIZE` config to support LE Set Extended Advertising Data command.
+
 See :ref:`bluetooth samples section <bluetooth-samples>` for common information
 about bluetooth samples.
 
@@ -55,6 +71,11 @@ to enable antenna switching. GPIOS are used by Radio peripheral in order followi
 indices of :code:`dfegpio#-gpios` properties. The order is important because it
 affects mapping of antenna switch patterns to GPIOS (see `Antenna patterns`_).
 
+Antenna matrix configuration for nRF5340DK SOC is part of child image that is run
+on network core. When :zephyr_file:`samples/bluetooth/hci_rpmsg` is used as network
+core application, the antenna matrix configuration is stored in the :zephyr_file:`samples/
+bluetooth/hci_rpmsg/boards/nrf5340dk_nrf5340_cpunet.overlay`.
+
 Antenna patterns
 ****************
 The antenna switch pattern is a binary number where each bit is applied to