doc: nrf_802154: Add changelog entry to main

Added back the changelog entry to the main section.
PR-1826

Signed-off-by: Richa Pandey <[email protected]>

Author: richabp

nrf_802154/doc/CHANGELOG.rst

@@ -10,6 +10,15 @@ Changelog
 All notable changes to this project are documented in this file.
 See also :ref:`nrf_802154_limitations` for permanent limitations.
 
+Main branch - nRF 802.15.4 Radio Driver
+***************************************
+
+Added
+=====
+
+* Added the new flag to :c:type:`nrf_802154_transmitted_frame_props_t` that allows to request encoding the transmit timestamp in the transmitted payload.
+  The feature can be enabled with the :c:macro:`NRF_802154_TX_TIMESTAMP_PROVIDER_ENABLED` configuration macro. (KRKNWK-20426)
+
 nRF Connect SDK v3.1.0 - nRF 802.15.4 Radio Driver
 **************************************************