docs: release: Add note on firmware loader mode

Adds a note on the new firmware loader operation type

Signed-off-by: Jamie McCrae <[email protected]>

Author: nordicjm

docs/release-notes.d/zephyr-firmware-loader.md

@@ -0,0 +1,4 @@
+- Added firmware loader configuration type support for Zephyr, this
+  allows for a single application slot and firmware loader image in
+  the secondary slot which is used to update the primary image
+  (loading it in any way it sees fit e.g. via Bluetooth).