Make it clearer somehow that tutorial examples are incomplete

[Rich-Harris]

A couple of times people have reported the tutorial as being 'broken', when in fact they just haven't completed the chapter. I'm not sure how to make it more obvious that the chapter begins in an incomplete state in a way that wouldn't be obnoxious after a while

[fvsch]

Some examples seem to work out of the box, especially in the form elements + bindings part, because form elements do have their internal state. It can take some clicking around to notice that this internal state is not reflected in the component state.

Not sure what's a good way to signal that to users.

[RAYDENFilipp]

1. I could tell that the Actions/Adding parameters chapter is incomplete.

2. Svelte: options chapter needs some exemplified clarification since there are different options available that are not clear for a beginner what should they do.

[Conduitry]

Optimistically closing this, what with the more prominent Show Me button in #3789.