doc: changelog: Add an entry for new doc

New doc about storing nRF70 firmware patches in external flash.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>

Author: krish2718

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -645,6 +645,9 @@ cJSON
 
 Documentation
 =============
+* Added:
+
+  * A page on :ref:`ug_nrf70_developing_fw_patch_ext_flash` in the :ref:`ug_nrf70_developing` user guide.
 
 * Added