Java usage documentation

[rubixhacker]

Please add documentation for how to call this from Java, otherwise an implemententer would need to understand how Kotlin extension functions are compiled to Java bytecode.

For example

val observable = call.toObservable()

would be

Observable<?> observable = Callkt.toObservable(call)

[Jawnnypoo]

Ahh thanks. Added some docs, changed the name so it would make more sense. 👍