Consider mentioning the Intern testing framework

[Intern](https://github.com/theintern/intern) has been using Istanbul internally for instrumentation for several years, and the soon-to-be-released Intern 4 also works with nyc.

Instrumentation is on by default in both the current and dev release. Both versions allow instrumenter options to be set with an `instrumenterOptions` property. In the current 3.x version the files that are covered are controlled by an [`excludeInstrumentation`](https://theintern.io/docs.html#Intern/3/docs/docs%2Fconfiguration.md/excludeinstrumentation) property, and in version 4 it's managed with the [`coverage`](https://theintern.io/docs.html#Intern/4/docs/docs%2Fconfiguration.md/coverage) property.