Add rx/js examples to documentation

[paarthenon]

From personal experience, variant works smoothly with observables. We should capture this experience with examples and put them in the docs, under the related libraries section.

https://paarthenon.github.io/variant/docs/next/libraries/rxjs

I use these to create live streams of a protocol and its augmented form, using variant for the transformation. It would be nice to illustrate that.