I have seen several questions asking for references that someone (or more than one) has marked as too broad. E.g. https://stats.stackexchange.com/review/close/190889 asks for references about using machine learning to build a trading portfolio.
I fully agree this would be too broad if the OP was asking for a solution to the problem, but he/she is not; they just want a place to get started.
I don't see how this is too broad, but perhaps I am missing something.