this function means that if other node want to add this node, othernode's unflip and flip readHeadSet should add to corresponding set in thisnode. Different with merging offset, adding offset will change scale instead of keep relative distance unchanged. So here is two situations:
1. add unflippset:
New_Offset(othernode's unflip set) = (Length(this_internal_kmer)/Length(that_internal_kmer)) * Old_Offset(othernode's unflip set)
2. add flipset:
First, flip Offset(othernode's flip set) = (Length(this_internal_kmer) - 1 - Offset(othernde's flip set))
Second, use option(1) to calculate New_Offset(othernode' flip set)