Adds a note on how to configure and what to beware of when
disabling mutex support in a multithreading application
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>
Adds documentation for the retention subsystem and boot mode
interface. Also marks the retention subsystem as experimental.
Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>