doc/release-notes: serial recovery fix

Added record on the fix.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>

Author: nvlsianpu

docs/release-notes.d/fix-serial-recovery-progressive-erase.md

@@ -0,0 +1,4 @@
+- Fixed serial recovery with progressive erase for MCUboot modes of single
+  updatable slot (MCUBOOT_SINGLE_APPLICATION_SLOT, MCUBOOT_FIRMWARE_LOADER,
+  MCUBOOT_SINGLE_APPLICATION_SLOT_RAM_LOAD) which was previously failing due to
+  attempts to access a non-existent image status fields area.