Add a question on other language support to an FAQ

[jonathanmetzman]

We've gotten enough questions on this that it makes sense to have a ready answer on whether ClusterFuzz supports languages other than C/C++.
It should mention:

1. How rust (and possibly other LLVM langs) works and go will probably be added.
2. Why fuzzing other languages probably won't serve the same function as fuzzing C/C++
3. What needs to be done to add support for another language.