[analyzer] Documentation of Container and InteratorModeling

Hi,

ClangSA has checkers which model and diagnose errors related to containers and iterators (currently in alpha). Their design goals, motivations, and implementation limitations are not sufficiently clear to continue with their development. Anyone related (or interested) is more than welcome to join the discussion on the WIP review page: https://reviews.llvm.org/D91948.

Thanks,

Endre