applications: nrf_desktop: Add note about version bump for B0

Jira: NCSDK-27889

Signed-off-by: Mateusz Kapala <[email protected]>

applications/nrf_desktop/bootloader_dfu.rst

@@ -89,6 +89,10 @@ The B0 bootloader additionally requires enabling the following options:
     The nRF Desktop application with the B0 bootloader configuration builds two application images: one for the S0 slot and the other for the S1 slot.
     To generate the DFU package, you need to update this configuration only in the main application image as the ``s1_image`` image mirrors it.
 
+.. note::
+    To ensure that update image will be booted after a successful DFU image transfer, the generated update image's version number must be greater than the version number of application image running on device.
+    Otherwise the update image can be rejected by the bootloader.
+
 .. _nrf_desktop_configuring_mcuboot_bootloader:
 
 Configuring the MCUboot bootloader