doc: matter: add section on packet buffer pool size configuration

Mention `CONFIG_CHIP_SYSTEM_PACKETBUFFER_POOL_SIZE` Kconfig option.

Signed-off-by: Adrian Gielniewski <adrian.gielniewski@nordicsemi.no>

doc/nrf/protocols/matter/getting_started/memory_optimization.rst

@@ -417,6 +417,13 @@ To use a dynamic heap size on your Matter device, set them both to ``n``.
 The static heap size means that you can define the maximum heap size for your application by setting the :kconfig:option:`CONFIG_CHIP_MALLOC_SYS_HEAP_SIZE` Kconfig value.
 You can also adjust the heap dedicated for MbedTLS purposes by setting the :kconfig:option:`CONFIG_MBEDTLS_HEAP_SIZE` Kconfig option value.
 
+Packet Buffer Pool Size
+-----------------------
+
+The Matter application uses a fixed size pool for packet buffer memory management.
+The pool size is determined by the :kconfig:option:`CONFIG_CHIP_SYSTEM_PACKETBUFFER_POOL_SIZE` Kconfig option.
+You can adjust the pool size to reduce the memory usage of your application, however that may have a negative effect on the performance of the application.
+
 .. note::
    The Thread protocol has a separate configuration for memory allocation.
    See :ref:`thread_configuring_messagepool` in the Thread documentation for more information.