docs(menu): add example of nested menus using dynamic data

Bug, feature request, or proposal:

Feature Request - Menu Docs

What is the expected behavior?

The docs would include an example of building a menu from a data structure similar to the radio button docs.

What is the current behavior?

The menu docs only include a nested menu example using static HTML.

What are the steps to reproduce?

Working on a Stackblitz demo atm...

What is the use-case or motivation for changing an existing behavior?

This is a common use case for building application menus, especially for business applications. The data may come from a config file, a REST API, or some other source but it is very often not static and does not align with a static HTML example.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Angular 4.4.3 TypeScript 2.3.4 Chrome 61 OS X El Capitan

Is there anything else we should know?

Thank you for your hard work on this library!