doc/release-notes: serial recovery fix

Added record on the fix.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
Signed-off-by: Jamie McCrae <jamie.mccrae@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 attempting to access non-existent image status fields.