fix:3040: Add comment about serverdown backoff delays

    private static final String TAG = NotesRepository.class.getSimpleName();

    // Delay between first ServerDownException occurs, and next synchronisation attempt: 5seconds.

    private static final long MIN_DELAY_AFTER_FAILED_SYNCHRONIZATION = 5000L;

    // MAX backoff delay after a ServerDownException: 24 hours

    private static final long MAX_DELAY_BETWEEN_SYNCHRONIZATIONS = 24 * 60 * 60 * 1000;

    private static NotesRepository instance;