In order to be consistent with the rest of the subsystems, remove "subsystem" from the title. Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>
Add documentation for two closely-related subystems: dfu and mgmt, which are currently undocumented. Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>