Update documentation of Track Titles around presence of performer and writer in title

At present a user can read either or both of
https://musicbrainz.org/doc/Style/Classical/Track/Title
and
https://musicbrainz.org/doc/Style/Titles
and, while following those guidelines, create track titles that include the performer and/or the writer.

The utility of these documents would be increased if this was not the case.
Editors, especially beginners, could self-regulate better.
Mentors of new users could point to the relevant section in the documentation and not have write about "normal practice".