add tutorial about using babel-plugin-istanbul with babel-plugin-rewrie

[bcoe]

see: https://github.com/speedskater/babel-plugin-rewire#istanbul

It causes a fairly hard to diagnose bug if these plugins are used in the wrong order, it would probably be worth adding a brief tutorial on this topic -- so that we have something to point people to.

CC: @Stupidism

[bcoe]

CC: @speedskater

[JaKXz]

Related tweet by @hzoo: https://twitter.com/left_pad/status/852293895371329539