Add example on how to use together with APIs that can have a CLI

I am really interested in using Cursive for a little pet project I have where I'm making a "banking" interface with transactions, bank acounts, etc. I've tried fiddling around with Cursive but I can't make it work properly due to not knowing how it all fits together. At the start of the CLI bin I'm initializing some structs holding various things, then after processing all the data I'm adding new bank accounts etc via functions on one of the structs. So what I have is something I believe every rust program using e.g clap has and implements.

So to the problem.

None of the examples use any sort of outer "variables", instead they show how to build a UI according to a known-at-compile-time, "static", framework. Take the [menubar example](https://github.com/gyscos/Cursive/blob/master/examples/menubar.rs), here we show how an user can make a menubar with subtrees and items, but not how to e.g make the Recent item actually show anything useful and dynamic. The examples are only showing how to make views do stuff, (which is helpful when learning how Cursives standard views work), but it does not actually show how to use a crate together with Cursive.