Add `T_subseq_isfinite` Note to `normalize` Docstring

[seanlaw]

In some functions like, core.mass or motifs.match, it is possible to supply an optional T_subseq_isfinite parameter IFF normalize=False. Therefore, we should add a note to the normalize docstring to express this option.

Note that we should NOT recommend replacing M_T with T_subseq_isfinite as this is confusing.