A typescript example for further clarification

[bbarker]

See http://stackoverflow.com/questions/41910459/in-cycle-js-collections-how-does-the-second-sources-stream-relate-to-the-first/41915677#41915677 for related question that might help improve docs further

[Widdershin]

Hi @bbarker,

I appreciate your contribution, and I definitely think we need to expand the documentation for how the add$ argument works, and how it might be used.

While I enjoy using TypeScript, I fear that mixing TypeScript examples in with the rest of the documentation might be intimidating to anyone unfamiliar with the TypeScript syntax.

Could you please rewrite this documentation in JavaScript, and perhaps add a section with any other useful TypeScript information at the bottom of the documentation?