LsiModel ( & maybe others) should generate docs for essential special-methods (like __getitem__ etc)

[gojomo]

Answering someone's LSI question, I noticed that none of the Gensim docs around LSI point out that you need to use bracket-indexed access to get the LSI topics for a BoW doc - not the class doc, or the tutorial. A user would need to know or intuit that's the Gensim convention from elsewhere.

Without understanding the auto-doc config exactly, I suspect LsiModel needs some config file like the one in poincare.rst:

https://github.com/RaRe-Technologies/gensim/blob/develop/docs/src/models/poincare.rst

...which enabled doc-generation for special-members. Perhaps, it'd even be appropriate to toggler generation of such docs globally, if possible, given the centrality of the bracket-accessing to some of the Gensim classes' APIs. If that's not possible/wise, a survey of which classes – (a) implement specials that are essential to thei use; & (b) don't yet have doc-comments, or generate web docs for those methods – should be done with the oversights fixed.