Add learning resources for people new to C++

[rileyjmurray]

RandBLAS makes modest use of C++ features. However, the few features we use might create confusion for people used to writing numerical code in C. It's also likely that projects which build on RandBLAS will want to use fancier abstractions (particularly object-oriented programming) available in C++. In view of this, I think it would be nice to have a C++ tutorial that's more tailored to our users than the thousands of C++ tutorials that already exist.

For example, RandBLAS' main use of C++ features is templating numerical precision and the random number generator. I've seen people write code that calls templated functions with redundantly specified the template parameter. It would be nice to have a short writeup explaining when that is or isn't needed.