Surface the "lede" in documentation

[Siddhartha Kasivajhula]

It has been pointed out that it's hard for newcomers to get an idea of what Qi is for from looking at the introductory docs. The "lede is buried."

@benknoble suggests:

perhaps we need a little “teaser”: tired of writing <blah>? The threading form makes it easier to follow . But wait, there’s more: multiple values <example>, etc.

Here's an excerpt of the original feedback from DehiDehi on Discord:

Some feedback, I read the beginner QI docs for 15 minutes and it failed to illustrate what the point is IMO.
It would definitely help to have an earlier concrete and useful example.

Unfortunately all I took away is : it's some sort of syntactic sugar over the streams pattern.
and : it's way over a racket beginner's head

[...]

Teaser examples would be great