Simplify examples of Smartdown flows

Many of the original examples were incomplete, missing features or hard to follow.
This replaces them with a simpler and easier to understand example, while pointing
to where real Smartdown content will live in the future
Do we want these to stay in sync with the latest additions to the gem (eg next steps), or are we happy with them getting out of date over time (or at least missing examples of some of the smartdown possibilities?)