Document wrapping insert with select

[raddevon]

I thought we already had this documented — and I believe it is in the book — but it's a pretty fundamental concept and should also be documented here.

[scotttrinh]

We added some details about this to the edgedb-js docs (see geldata/gel-js#838). To that end, makes sense to add this to the update docs as well, yeah?

Maybe we also need to update select in a way that makes this pattern intuitive?

[elprans]

Let's also offer an example of a with style, which I personally prefer as a better-looking formulation:

with
   NewHero := (insert)
select
   NewHero {
      id,
      name,
   }

[raddevon]

@scotttrinh Good idea. Maybe we just cover delete too while we're in there and complete the set…

[raddevon]

@scotttrinh Added this to the update docs as well. It looks a little different because that page is surprisingly different in structure from the select one, but I tried to match the structure of the update page while keeping the new information in basically the same shape it has on the select page. (Turned out, delete already mentions this.)

Would you take a peek at the new stuff and make sure it looks reasonable before I merge?

[scotttrinh]

New changes look good!