doc: release_notes: add note about nRF54LM20 FLPR

Support for nRF54LM20 FLPR was added.

Signed-off-by: Marcin Szymczyk <[email protected]>

Author: masz-nordic

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

@@ -115,7 +115,7 @@ Developing with custom boards
 Developing with coprocessors
 ============================
 
-|no_changes_yet_note|
+* Added support for the nRF54LM20 FLPR.
 
 Security
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