applications: serial_lte_modem: Documentation corrections

Corrections to SLM documentation.

Signed-off-by: Markus Lassila <[email protected]>

Author: MarkusLassila

applications/serial_lte_modem/doc/slm_data_mode.rst

@@ -106,7 +106,7 @@ For more information, see the `Data mode control #XDATACTRL`_  command.
 Flow control in data mode
 =========================
 
-When SLM fills its UART receive buffers, it enables the UART hardware flow control, which disables UART reception.
+When SLM fills its UART receive buffers, it disables UART reception. If ``hw-flow-control`` is enabled for the UART, hardware flow control is imposed. Without hardware flow control, the SLM application will drop incoming data while the UART reception is disabled.
 SLM reenables UART reception when the data has been moved to the data mode buffer.
 If the data mode buffer fills, the data are transmitted to the LTE network.
 

applications/serial_lte_modem/doc/slm_description.rst

@@ -310,6 +310,9 @@ The following configuration files are provided:
 
 * :file:`overlay-carrier.conf` - Configuration file that adds |NCS| :ref:`liblwm2m_carrier_readme` support.
   See :ref:`slm_carrier_library_support` for more information on how to connect to an operator's device management platform.
+  With the ``thingy91/nrf9160/ns`` board target, you must additionally pass the sysbuild option ``-DSB_CONFIG_THINGY91_STATIC_PARTITIONS_LWM2M_CARRIER=y`` to fit the application in the flash memory.
+  This means that you will need an external debug probe to program the application.
+  See the :ref:`programming_thingy` for more information.
 
 * :file:`overlay-carrier-softbank.conf` and :file:`sysbuild-softbank.conf` - Configuration files that add SoftBank configurations needed by the carrier library.
   Used in conjunction with :file:`overlay-carrier.conf`.